in a part in the movie, tate gets mad at his grandparents, and goes outside to a group of 10 year old girls playing jumprope. he tells them how mad he is at his grandparents, and starts playing jumprope with them. but...isnt tate like, 16, 17?? why is he hanging out with little girls? is it because he didnt have any friends his own age?
If you notice, when we're first introduced to Tate, we find him examining pictures of Black individuals presumably NOT from North America that he ascribes very mundane suburban American names to. When we find him speaking to the little girls, the one he appears to be closest to and her friend are African American. The pictures Tate has are of African people that he ascribes American names to, thus, they too are African American. He's said to "think differently," and these different thoughts may have something to do with a strange fixation with African/American. That, however, is simply conjecture on my part.
Another reason could be due to the fact that, though, he is intelligent, he isn't mature. We see his immaturity bleed through when he plays Scrabble with his grandpa and in the manner that he addresses his grandmother. His intelligence and aforementioned 'different thinking' isolate him from peers (though, he does have friends his own age. He is after all friends with Shawn, Claude and Peaches). His immaturity helps him bond with the young girls and they possess the same naivety and innocence he has. He is very sadistic and cruel, but there are facets of him which show how undeveloped he is emotionally.
It's all up to interpretation, of course, but that is my take on things. Hope it helps.
Also, from a purely story-writing standpoint, this was sort of a nice moment for the audience to see that Tate isn't all bad and win back their sympathy a little bit after that incident with Legs and Grandma.