This paper argues that when young children are given an opportunity for their voice to be heard, they are competent communicators and social agents who can co-create cultural practices as theory makers. The paper draws on video recorded data from a small study that focussed on how young children (3-5 years) participated in an end-of-year cultural celebration in an early childhood education setting in Australia. The children organized a party, invited Santa Claus to visit, and setup a special place where they could hold conversations with Santa. Video recorded data of the conversations initiated by the children with Santa Claus were transcribed and analysed using the fine-grained interactional tools of ethnomethodology, conversation analysis and membership categorization analysis. Analyses identified children's competence as active social agents who challenged Santa's authenticity through checking his appearance, knowledge testing and, suggesting he was not the 'real Santa'. This evidence of children's capacity to authenticate cultural experiences demonstrates that incorporating children's voice in the co-creation of culture fosters children's opportunities to make and interrogate theory.