Grooming or trying to nurse?

Larger Grey Kitten has been somewhat harassing the smaller kitten by grooming his neck rather aggressively and kneading on him. The smaller one takes it for a while but then gets pissed and bites him. The smaller one has been doing a bit of licking too but it's mostly the larger one. It wasn't so cute when I saw the larger one licking the smaller one's butt. That was not caught on film. The licking continued for quite some time and then I discovered that the little one's neck was soaked so we separated them but the larger one kept going back for more. Smaller kitten had to thoroughly groom himself and now they're sleeping in separate baskets.