This paper follows undergraduate students' engagement with the concept of childhood presented to them during a year-long childhood and youth studies module. Through the application of "threshold concepts" as concepts which transform students' understandings of a subject, the challenges of learning new ideas or concepts of childhood are described. Findings from the qualitative research presented show students' prior understandings are deeply embedded. The conclusion discusses the pedagogical implications of students "unlearning" prior knowledge and suggests effective practice in encouraging a more reflective approach. Although discipline specific, the findings will be useful to the teaching and learning of concepts that challenge or undermine students' personal understandings of them.