The present work intends to analyse how pre-school aged children experience the re/construction of a 'gender identity' and the processes that create it as an essential, factual, and unchangeable reality -- therefore, suspect. Given the growing importance of 'gender identity development' in child development literature, as well as the arising voices of 'gender non-conforming' childhoods, this theme seems particularly relevant when faced with the limitations imposed by macrosocial discourses of cisheteronormativity. Using grounded theory and ethnography, the re/construction processes were observed in a mixed-age kindergarten classroom in Porto and analysed through the feminist lens of gender performativity. It was possible to observe the following dimensions: clothing and accessories as performative marks of gender; beauty and its role in constructing femininities; play as a regulatory fiction, that is both shaped by and constructs gender differences; gender borders and how they can be reinstated, negotiated or defied.