I am working on controlled experimental approaches with the 5 year old. He has been interested in how mommy and daddy as engineers turn their designs in our heads into things. He has been asking questions hitting on the scientific method, like "how do you know how much to add..." I want to explain to him about setting a starting point, what an experimental matrix is, and how he can record outcomes from each experiment in the matrix to make conclusions about cause and effect. My little dude will understand the value of changing one variable at a time from this engineering mom.