Bronfenbrenners Process-Person-Context-Time model was used to examine the relationships among the process of negative parenting, the person characteristics of child temperament and early aggressive behaviour and the contexts of family income (in)adequacy and maternal depression from infancy to school entry and their effects on the outcome of aggressive behaviour in boys at school entry. The sample included 361 boys in two-parent families who participated in the Canadian National Longitudinal Survey of Children and Youth (NLSCY). Structural equation modeling was used with a repeated measures longitudinal design. The model explained 43% of the variance in boys aggressive behaviour at school age. The results indicated that, by preschool age, boys and mothers behaviours are well established, and that process, person, and context variables all influence the persistence of boys aggressive behaviour. The strength of the effects of these variables increased with their proximity to the developing child and decreased over time. By school age, concurrent effects were not significant. The addition of the contextual variables resulted in ill-fitting models. Modification indices suggested the ill fit was localized in modeling the persistence of maternal depression, and not in the relationship between maternal depression and the other variables in the model. Modification indices also suggested there may be reciprocal effects between boys aggressive behaviour and both negative parenting and maternal depression, but this was not tested. Future research using a cross-lagged panel design could clarify these relationships. This study contributes to a growing body of research on the development of aggressive behaviour in children and underscores the importance of examining the contribution of the multiple levels of process, person, context, and time to the development of aggressive behaviour. Findings of this study provide evidence that the effects of proximal processes and proximal contexts on the development of boys aggressive behaviour are strongest in infancy and toddlerhood, and their consequences extend through to school entry. Initiating prevention and intervention efforts in early childhood that provide parents-to-be and parents of young children with practical direction in ways to engage in positive and responsive interactions with their children would do more to reduce the development of aggressive behaviour in children than would later interventions aimed at changing entrenched behaviours in both parents and children.

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The current study examined the mediating role of possible food preferences on the temperamentweight relationship among 18-month-old toddlers. Parents of 37 typically developing toddlers completed the Early Childhood Behavior Questionnaire (ECBQ). During a lab visit toddlers’ weight and recumbent length were measured and recorded. Toddlers also completed a sequential touching task to examine their ability to categorize a healthy group of foods and an unhealthy group of foods. The only temperament measure found to associate with both child weight status and food categorization was inhibitory control. Toddlers’ food categorization was not found to mediate the relationship between inhibitory control and their weight status. The results of this study suggest that there is a continued need for a nonparent report measure of food preferences.

According to previous research, internalizing and externalizing problems tend to be comorbid or co-occur at different ages in development (Angold, Costello, & Erkanli, 1999). The question that this dissertation addresses is how and why internalizing and externalizing problems, two disorders that represent separate forms of psychopathology, co-occur in children. This is an important question for the developmental psychopathology perspective because an appreciation of the concept of co-occurrence is essential for explaining the development and taxonomy of internalizing and externalizing psychopathology, and for understanding the etiology and course of these symptoms (Achenbach, 1990). Attempts to explain co-occurrence have proposed that co-occurring psychopathology might represent distinct, meaningful syndromes (Angold & Costello, 1992; O’Connor et al., 1998), and in support of this idea, evidence of the existence of pure and co-occurring internalizing and externalizing problems has been found (Keiley et al., 2003). However, no previous study has identified heterogeneous developmental patterns of pure or combined internalizing and externalizing problems within a dynamic framework by taking trajectories of change into account. This dissertation uses data from the NICHD study of Early Child Care to explore the co-occurrence between internalizing and externalizing problems from age 2 to 12 with the use of Latent Class Growth Analysis. The sample included 1232 children (52% male). Different groups of children exhibiting low/normative, pure internalizing, pure externalizing, and co-occurring internalizing and externalizing problems across the 10 year period were identified. The higher risk groups deviated from the low/normative group in terms of antecedents, SES risk, medical risk, difficult temperament, and home environment. Moreover, children who exhibited pure moderate externalizing problems, and children who exhibited chronic externalizing problems, with and without co-occurring internalizing problems, engaged in more risky behaviors and were more likely to have friends who also engaged in risky behaviors. Furthermore, the pure chronic externalizing group and the groups scoring high on internalizing problems, with and without co-occurring externalizing problems, were more asocial with peers. Finally, children exhibiting chronic co-occurring externalizing and internalizing problems were more excluded by peers in comparison to the rest of the sample’s population.

The presented dissertation consists of both a quantitative part and a qualitative part. The quantitative part deals with the relationship between 5-HTTLPR S/L, MAOA H/L, and COMT Val158Met polymorphisms, the stress reaction of new-born infants after a heel stick blood draw (measured by determining salivary cortisol at three time points) and temperament assessed at age three months by Rothbarth's Infant Behavior Questionnaire-Revised in a sample of 84 infants. Observed polymorphisms were related both to the course of the stress reaction and to temperament. The short allele of serotonin transporter polymorphism was connected to higher scores in the secondary scale of Negative Affect and lower scores in the secondary scale of Attention/Regulation. Homozygotes for the more active allele of MAOA polymorphism (HH) had the lowest scores in Negative Affect compared to both of the remaining groups, they also had higher scores in the secondary scale of Extraversion and Attention/Regulation and a greater decrease of cortisol in comparison to HL heterozygotes. The presence of low-active L allele predisposed their carriers to higher scores in Negative Affect and lower scores in Attention/Regulation. LL homozygotes had the highest increase of cortisol after a heel stick blood draw. The Met allele of COMT Val158Met polymorphism was connected to higher Extraversion and Attention/Regulation and a greater cortisol decrease. It was possible to predict all three secondary scales of IBQ-R from the stress reaction after the heel stick blood draw. Negative Affect was predicted by a higher increase and a lower decrease of cortisol. Extraversion and Attention/Regulation were predicted by a greater cortisol decrease. The magnitude of cortisol decrease partially mediated the influence of COMT Val158Met polymorphism on Extraversion. The qualitative part of the dissertation is a multi-casuistic study of six couples parenting infants with difficult temperaments. It is based on semi-structured interviews that were analysed in accordance with qualitative procedures. The most difficult infant displays to manage were unsoothable crying in the first six months and early sleeplessness and a later escalation of sleeping problems. Mothers were esentially not able to gain control over the amount of crying, but some of them managed to influence their experience to achieve a greater acceptance of it. To do this, it was necessary for them to eliminate their feelings of failure in the parental role. The parents' biggest dilemma concerning their infants' sleeping problems was whether to use the "cry it out" strategy or not to manage them. For some parents parenting a difficult infant was an opportunity to re-evaluate their approach to parenting and the parental role, significantly broadening the concept of both. Caring for a difficult infant significantly strained the marital relationship; four couples experienced marital crisis during the care of their child. The father's involvement in infant care seemed very important in this respect. Insufficient involvement led to dissatisfaction in the mother, the way the mother communicated her demands further influenced the marital relationship. Particular behaviour that the mother understood as the father's involvement in infant care emerged.

La relation mère-enfant a une influence sur le développement de l’enfant. Cette étude vise principalement à vérifier si la sensibilité maternelle modère l’expression du tempérament difficile de l’enfant à 9 mois. Elle vise également à vérifier si la relation d’attachement sécurisante / insécurisante modère le développement de comportements perturbateurs chez les enfants de 24 mois. Les données de l’étude La mère veille ont été employées. L’échantillon compte 96 mères adolescentes, âgées entre 14 et 19 ans, provenant de deux (2) milieux distincts : une école spécialisée pour mères adolescentes et un foyer de groupe. Des analyses de régression multiple n’ont pas confirmé l’effet modérateur de la sensibilité maternelle sur l’expression du tempérament difficile de l’enfant à 9 mois. Les analyses ont cependant montré un effet prédictif de l’attachement sécurisant / insécurisant sur le développement des comportements perturbateurs à 24 mois. En effet, un enfant qui a développé un attachement sécurisant envers sa mère est moins à risque d’émettre des comportements perturbateurs à l’âge de 24 mois. Les résultats ne permettent cependant pas de confirmer que l’effet observé est modérateur. / Mother-child relationship has an influence on children’s development. This study aims to verify if maternal sensitivity moderates the expression of a difficult temperament at 9 months, and if a secure or insecure attachment relationship with the mother moderates the development of disruptive behaviors in 24 month-old children. Data come from the study «La mère veille». The sample includes 96 teenage mothers (14-19 years old) recruited from two different resources: A specialized school for teenage mothers and a group home. Multiple regression analyses did not confirm the moderating role of maternal sensitivity in the expression of child difficult temperament at 9 months. Analyses nevertheless demonstrated a predictive relation between secure/insecure attachment and disruptive behaviors at 24 months: Children who had developed a secure attachment relationship with their mother were less likely to exhibit disruptive behaviors at 2 years. The current results did not support the hypothesis of a moderating role of attachment security.

La relation mère-enfant a une influence sur le développement de l’enfant. Cette étude vise principalement à vérifier si la sensibilité maternelle modère l’expression du tempérament difficile de l’enfant à 9 mois. Elle vise également à vérifier si la relation d’attachement sécurisante / insécurisante modère le développement de comportements perturbateurs chez les enfants de 24 mois. Les données de l’étude La mère veille ont été employées. L’échantillon compte 96 mères adolescentes, âgées entre 14 et 19 ans, provenant de deux (2) milieux distincts : une école spécialisée pour mères adolescentes et un foyer de groupe. Des analyses de régression multiple n’ont pas confirmé l’effet modérateur de la sensibilité maternelle sur l’expression du tempérament difficile de l’enfant à 9 mois. Les analyses ont cependant montré un effet prédictif de l’attachement sécurisant / insécurisant sur le développement des comportements perturbateurs à 24 mois. En effet, un enfant qui a développé un attachement sécurisant envers sa mère est moins à risque d’émettre des comportements perturbateurs à l’âge de 24 mois. Les résultats ne permettent cependant pas de confirmer que l’effet observé est modérateur. / Mother-child relationship has an influence on children’s development. This study aims to verify if maternal sensitivity moderates the expression of a difficult temperament at 9 months, and if a secure or insecure attachment relationship with the mother moderates the development of disruptive behaviors in 24 month-old children. Data come from the study «La mère veille». The sample includes 96 teenage mothers (14-19 years old) recruited from two different resources: A specialized school for teenage mothers and a group home. Multiple regression analyses did not confirm the moderating role of maternal sensitivity in the expression of child difficult temperament at 9 months. Analyses nevertheless demonstrated a predictive relation between secure/insecure attachment and disruptive behaviors at 24 months: Children who had developed a secure attachment relationship with their mother were less likely to exhibit disruptive behaviors at 2 years. The current results did not support the hypothesis of a moderating role of attachment security.