My 7yo ds has come home from school today and said a boy in year 3 keeps calling him "fatty". Now ds is quite big for his age but is not fat. He wants to retaliate but is scared to call names in school for fear of getting into trouble (bless him). Do I tell him it's okay to call this lad names as long as they're not too rude or should he keep schtum and let it eat away at him (no pun intended)