The first time I became aware of anybody's skin color was at age five in kindergarten. My mom had come to pick up me and my twin brother, and one of her girlfriends noticed that we were friends with one of the black kids in the school. My mom's girlfriend remarked, "Isn't that sweet? They're friends with a little black boy."
Even at five I found that remark unusual -- or maybe it was because I was five. My brother and I played with kids because we connected on a "fun" level. It didn't matter if they were different, or for that matter the same, when it came to anything physical. To us, fun was fun. If you had fun with someone, you played with him. If you didn't, well, you found someone else to play with.
That's the way it still is in kindergartens today. Kids are just kids, and they play with the kids who simply like to play with what they like. That's it. That's how friendships are formed.
Children don't see a difference. But as they grow, the world surely teaches them the difference.
There appears to be a movement afoot today to instruct children as young as kindergarten-age in "diversity" in hopes that they'll learn "tolerance" early enough to affect their adult lives. In other words, as soon as possible, some adults seem to want to saddle kids with their own guilt or phobias or angst. Good-bye, fun.