I was a chubby kid, a voluptuous teen, and now a very fat adult. I’m content with that, but yes, children can be very very cruel.
My sister had twin girls 11 years ago. They were born 9 weeks early. One girl (E) was born with a disease that destroyed her liver, and she had a liver transplant at 7 months old. The other girl (L) had a two-cord umbilical cord and was born just over 1 lb. We feel ourselves to be extremely lucky to have both girls still alive and doing well at 11 years old.
E had some later problems with the transplant, and ended up with an enlarged spleen, so she has a tiny bit of a belly. L has eating problems (and always will), so she’s very, very thin. Both girls are extremely tall for their age. In school, L gets teased for being too thin, and E gets teased for being too fat. Fortunately, my sister went through the same diet misery that I have, and refuses to raise her daughters with the same screwed-up mentality about food that we have, so they get support at home. But the teasing is the same. No matter what size you are, no matter what you do or say, kids are going to be teased at school. The best you can do is give them all of the love and support outside of school that they need. Just make sure that *someone* tells them that they are loved.
No child should be teased on all sides, only to get berated at home for the same thing.