This paper reports on a mixed-model case study of designing and implementing a constructivist teaching intervention about reproduction and physical family resemblance for young children. The objective of the study was to explore whether the ways that preschoolers reason about the resemblance between offspring and parents can be improved with a teaching intervention that introduces a rudimentary idea of genes through reproduction. The participants were 60 preschoolers (age 5-5.5 years) from public kindergartens of Patras. The qualitative analysis of their pre- and post semi-structured interviews showed a remarkable improvement in their reasoning, which was found to be statistically significant as well. After the three-part teaching intervention, children appeared to recognize the biological contribution of both parents to a child's creation. Moreover, most of them appeared able to attribute a child's species and body traits to the parental genes passed to the child through reproduction and not to the parents' or child's intention.