This study aims to examine if children have a coherent, naïve theory or, alternatively, only fragmented knowledge of prenatal development. Following Karmiloff-Smith's theory of representational redescription, it examines whether these theories are influenced by age related constraints in representational flexibility. Children aged 6-13 (N=317) filled out a forced-choice questionnaire and completed two drawing tasks. Examination by latent class analysis indicates that children do have coherent theories on prenatal development for the changing morphology, but not for the changing bodily functions and that coherence of their mental model is increased by a preceding generative task. The observed mental models are characterized by different levels of representational flexibility.