Children’s early mathematics learning and development have become a topic of increasing interest over the past decade since early mathematical knowledge and skills have been shown to be a strong predictor of later mathematics performance. Understanding how children develop mathematical knowledge and skills and how they can be supported in their early learning could thus prove to be a vital component in promoting learning of more formal mathematics. In light of the above, with this thesis I sought to contribute to an increased understanding of children’s early mathematics learning and development by examining effects of playing different number games on children’s number knowledge and skills, and by investigating children’s representations of numbers on number line tasks. Two number game intervention studies were performed, and effects of three different number game conditions (linear number, circular number and nonlinear number) were investigated by examining 5- and 6-year-old children’s pre- and posttest performance on different numerical tasks. The findings indicate that playing number games in general support children’s development of number knowledge and skills, where the specific learning outcomes are affected differently depending on the type of number game utilized. To elucidate children’s representations of numbers, their performance on two different  umber line tasks have been analyzed using a latent class modeling approach. The results reveal that there is a heterogeneity in 5- and 6-year-old children’s number line estimations and subgroups of children showing different estimation patterns were distinguished. In addition, it is shown that children’s number line estimations can be associated to their number knowledge as well as to task specific aspects. The findings presented in this thesis contribute to the discussion of the value of selecting game activities in a conscious way to support children’s early mathematics learning and development. They also add to the discussion regarding the number line task and how children’s number line estimations can be analyzed and interpreted.