The notion of theory of mind is very prevalent among research into child development, with one of the core concepts being performance on tests of false belief. The individual influences that cause varying degrees of acquisition are of great interest in this field. The main aim of this study was to determine whether day care and sibling constellation had an effect on the theory of mind performance of young children. Thirty-six preschoolers aged 3-5 were tested on three false belief tasks. All three tasks involved the observation of a scenario, followed by a series of understanding and false belief questions. Children were given a false belief score and an understanding score for each task and a composite score for false belief. In addition, parents completed a questionnaire regarding any day care settings their child had attended including the nursery they were sampled from. Information on the ages and genders of any/ all siblings in the family household were collected. The results indicated that there was a positive relationship between day care and false belief score though not when the factor of age was removed. Analysis of false-belief scores between three year olds and four+ year olds revealed a highly significant discrepancy in their scores with four+ year olds performing significantly better on two out of the three tasks. Children with no siblings proved to be significantly better at false belief tasks than children with older siblings but this could be due to the fact that children with no siblings were significantly older than children with older siblings.