Yesterday, SO had the day off, so he was around and he was grilling some food for dinner. We have a son together, and our son is black and white. My 4yo is mexican and white.
Well, 4yo out of nowhere decided to start spewing off at the mouth saying "black guys can't be husbands and they're old and dirty"... I don't know if that's something that he can make up, but I drilled him for an hour off and on asking who said that to him or where he learned it from. I told him a million times nicely that he won't be in trouble, but I need to know because whoever that person is, I don't want around my SO, or my other son.
Note that we don't watch a lot of TV and when we do, it's cartoons.
4yo kept going from one person to the other, listing off people who told him this, to the point where I don't know what to believe because he went from my grandfather, all the way to my uncle, to his dad, and a few more people in-between.
I would just explain to him how that is not nice to say and simply not true, point out all the awesome things your SO does for him and you, and your other son and make it clear that if the things he was saying were true then your SO wouldn't do those nice things for him. Then I would just leave it be. I doubt he really knows what he is saying at this age.
Maybe drop it for a few days and when he brings it up again be very cool. Nonchalantly ask, "Oh really? Who told you that?" If he won't tell you, you are going to have to start talking to family. SMH! So sad!