Children frequently experience social ambiguity, where the context and expectations for an interaction are unclear. Responses to ambiguity can vary greatly, potentially due to children’s differing challenge and threat appraisals. Although we know children use information from their environments in the process of making appraisals, what specific information children use to inform their challenge and threat appraisals is still an open question. My dissertation aimed to examine factors that may contribute to children’s challenge and threat appraisals and subsequent social problem-solving behavior in ambiguous social contexts. These included the tendency to make challenge appraisals across discrete emotion contexts, emotion regulation ability, and different social motivations. To address these aims, I utilized an existing dataset from a larger study of children’s physiology and emotion regulation. The focus of this dissertation was on several tasks, including an interview about children’s previous experiences of different emotions, and three ambiguous social interactions in which (1) the experimenter wore a scary Halloween mask, (2) the child and experimenter took turns playing a game, and (3) the experimenter gave the child an unwanted prize. Interval coding (10-s intervals) captured the extent to which children used 4 social problem-solving behaviors: expressed positive affect, speech, laughter, and approach. Children’s appraisal tendencies were derived from their responses during the interview. Parent reports were used to characterize children’s emotion regulation abilities, shyness, and social disinterest. Data analysis included hierarchical multiple regression, Cox regression, and binary logistic regression. Results indicated that children’s challenge appraisals may relate to their social problem-solving behavior in some emotion contexts, but not others. This relationship was shown to be further qualified by the social nature of the appraisal made. Children’s emotion regulation, shyness, and social disinterest were not related to children’s appraisals, but were related to social problem-solving. Greater emotion regulation and shyness predicted quicker social problem-solving during the ambiguous scary task, whereas greater social disinterest predicted slower social problem-solving during the same task. In addition, shyness was related to less social problem-solving in general and in the ambiguous frustration task, and slower social problem-solving in the ambiguous frustration task. Finally, social disinterest was associated with less social problem-solving in general and in the ambiguous frustration task as well. This dissertation’s contributions are both methodological and theoretical. Novel methods included asking children to recall personally meaningful experiences in which they felt different emotions, and examining children’s in-vivo responses to ambiguous social situations. Overall, this dissertation contributes to our understanding how variations in children’s regulatory abilities and social motivations relate to the cognitive appraisal process and subsequent behavior, providing more insight into the long-term impacts of children’s earlier life experiences.