Supporting family conversations and children's STEM learning in a children's museum

•Families with 4- to 8-year-old children were observed in a building construction exhibit at a children's museum.•Families were randomly assigned to conditions that varied in terms of the instructions about a key engineering principle and elaborative question-asking that they received.•Effectiveness of the program was assessed across conditions and cultural groups.•Results have implications for understanding family conversation and children's STEM learning in families from diverse backgrounds.