My DS1 has just started school last week and has a birthday in a few weeks time. Obviously hasn't made any proper friends yet but we have organised him a birthday party with a small number of outside of school friends.
When asked who DS1 would like to invite to his party he is saying all the ones already invited from out of school and also one new friend from in school.
I think inviting this one new friend is fine, DH says it will cause "segregation " and problems at school.
Who is right
YABU: DH is correct, inviting only one friend from his new class will have social repercussions for DS1
YANBU: it's his party he can invite whoever he wants and won't cause any class related dramas