Cole was reading his new Lego book (in which all the characters are those little Lego people and all the settings are Lego pieces). He was pointing out that all of the Lego "people" had yellow faces except one of them who had an orange facee (in fact this wasn't true, the last little Lego guy was wearing a helmet with a visor that changed the apparent hue of his face).
Regardless, it seemed like a good teachable moment. So I said to my son, "Well, everyone's different. Some people have lighter skin and some have darker skin. And everyone's hair is a different colour. And some people are big and some are small."
"Why, mom?" he asked.
"Because of their genes," I replied.
He nodded sagely, "Some genes are big and some are small."