Personal note: I very sadly observed a 5-year-old act like this toward my 4-year-old daughter, who is black, not too long ago, and I watched his mortified dad fumble, unsure of what to do. Since then, we've come up with a few ideas. We can acknowledge we're not "post-racial," we can stop saying that we have a black president so there's no more racism, and we can affirm that this most certainly is a thing. Most importantly, we can talk to our kids, often and consistently, about race. Let's start with that and see where it takes us.