This thesis presents the results of an experimental study designed to examine whether children raised bilingually in Japanese and English from birth in Christchurch, New Zealand, exhibit the same morphological case and topic marking knowledge in Japanese as monolingual children in Japan. The participants were 34 children aged between five and eleven years who have been raised in a one-person one-language environment in an English dominant community. The study replicated previous studies on monolingual Japanese children, and involved two widely used paradigms for assessing a child’s grammar: picture selection, and elicited imitation. The responses of the children in this study were different from those reported in studies of monolingual children. In the picture selection tasks, some children in this study interpreted the agent-patient relationship based on the word order cue in the object-initial types of transitive sentences, whereas previous studies have demonstrated that monolingual children five years and older are able to interpret the agent-patient relationship in the same way as adults, using the case marking cue. Moreover, in the elicited imitation tasks, many children in this study re-analysed the topic-comment construction as a genitive possessive when the particles in the stimuli were masked with noise. This pattern has not been reported in any previous study. The results also revealed that there was a great degree of individual variation. The study suggests cross-linguistic influence from English on Japanese as a possible explanation for the difference between the children in this study and monolinguals. The phenomena observed in the results satisfies two conditions for cross-linguistic influence proposed by Hulk and Müller (2000) and Müller and Hulk (2001), because (i) English and Japanese overlap at the surface level in terms of the agent position in a canonical sentence and the possessive structure, and (ii) the problematic structures for some children in this study involved the interface between syntax and pragmatics in the C-domain. The study, however, has no principled explanation for the individual variation found because of a lack of data on the Japanese input and the child’s fluency, both of which are likely to affect simultaneous bilingual development.

This study concerns simultaneous bilingual acquisition (2L1) of Swedish-Brazilian children growing up in mixed-lingual families in Stockholm, with Swedish as their dominant language. Earlier studies on this language combination were not found. Not even were there any studies considering 2L1 children of the same age group as our main subjects (Anna 7;7,3–9;1,30, Maria 6;1,16–6;11,11). An analysis of their acquisition of Brazilian Portuguese (BP) as a weaker language (WL) was carried out in a Generative Grammar approach, mainly through the selective theory of language acquisition. The corpus consists of interviews with 2L1 children in a semi-longitudinal registration of their production. The focus of this analysis lies on the observation of three domains of BP grammar that differ morpho-syntactically from Swedish: verb inflection; VP as minimal responses; NP number and gender agreement. Three main research questions were formulated: 1) Are the simple and robust structures, provided by domestic input enough for triggering the functional categories (FC) of their WL? 2) If the FCs are activated, do they develop in the same sequence as a WL as they would in BPL1? 3) If the 2L1 children show any deviations in acquiring the grammar of their WL, is it possible to distinguish any influence from Swedish? To answer these questions a contrastive study was carried out, comparing the acquisition of BPWL with studies on 2L1 and BPL1 acquisition. The results show that the domestic input is enough for triggering the grammar of the WL, and that it was triggered and developed through a similar procedure to that of BPL1, although delayed. Contact with BPL1 input in Brazil was necessary to activate the children’s oral production. When using VPs for minimal responses it requires more than domestic input, and the influence of Swedish was reflected in the subjects’ use of sim ‘yes’ instead of VPs, as in this case grammar enters the domain of discourse at the syntax/pragmatics interface.