Toddlers don't know the meanings and implications of racial slurs.
Here's something I realized growing up in a pretty diverse environment. When I was young, I knew nothing about race and just played with pretty much any kid who was willing to play with me, and from what I could tell and remember most kids are the same. It's when we get older and notice the differences, we start mainly hanging around certain kinds of people, usually people that are more like "us." I heard racist or hateful comments all the time, I sorta knew what they meant or atleast the type of people they were meant for, but it wasn't till I was about 10 or most likely even older that I actually knew their true implications.
Just from that I can tell that little kids most likely can't be racist. The thought of racial superiority is something taught and will only get stronger if it is constantly re-enforced until they reach the age of realizing their social identity.