While recent reform-based efforts have shifted the emphasis towards engaging children in science practices, little research has considered how preschool-age children take first steps towards engagement in evidence-based explanations or modelling practices nor the role museum-settings might provide. Using a theoretical perspective that science emerges through interaction as it is practiced, we analysed videos of four [approximately]30-min programs for 3-to-5-year-old children at a small children's science museum. Findings suggest that the children's explanations, which were co-constructed with the museum educator, ranged in sophistication from an implicit use of evidence to an explicit use of evidence and use of reasoning. We also found that the children used modelling practices to support their development of evidence-based explanations both as a method to generate evidence and to communicate their explanations. An important factor in how we interpreted children's explanations and modelling practices was through their use of gestures, which they often used to indicate their evidence or other elements of meaning while communicating during the investigations. Our findings provide evidence for young children's initial entry point for co-constructed, evidence-based explanations as they were produced through interactions with the educator and peers.