My son is almost 6, and I just put him in a new school. Now he's a boy, so I'd probably treat my chubby little daughter differently, but I've honestly told him not to take shit from anybody.
Make friends, find kids that you have things in common with. At this age, they got to find kids they can talk and play with.
Don't talk to anyone you don't like.
Luckily, the main problem he has is arguing with friends that he does have about how so and so made him mad while playing, or how he doesn't like sharing toys.