This paper aims at exploring (a) whether preschoolers recognize that offspring share physical traits with their parents due to birth and behavioural ones due to nurture, and (b) whether they seem ready to explain shared physical traits with a "pre-biological" causal model that includes the contribution of both parents and a rudimentary notion of genes. This exploration is supposed to provide evidence for our next step, which is the development of an early years' learning environment about inheritance. Conducting individual, semi-structured interviews with 90 preschoolers (age 4.5-5.5) of four public kindergartens in Patras, we attempted to trace their reasoning about (a) whether and why offspring share physical and behavioural traits with parents and (b) which mechanism could better explain the shared physical traits. The probes were a modified six-case version of Solomon et al. ("Child Dev" 67:151-171, 1996) "adoption task," as well as a three-case task based on Springer's ("Child Dev" 66:547-558, 1995) "mechanism task" and on Solomon and Johnson's ("Br J Dev Psychol" 18(1):81-96, 2000) idea of genes as a "conceptual placeholder". The qualitative and quantitative analysis of the interviews showed overlapping reasoning about the origin of physical and behavioural family resemblance. Nevertheless, we "did" trace the "birth-driven" argument for the attribution of the offspring's physical traits to the biological parents, as well as a preference for the "pre-biological" model that introduces a rudimentary idea of genes in order to explain shared physical traits between parents and offspring. The findings of the study and the educational implications are thoroughly discussed.