For my son's birthday party I've had to limit the number of friends he can invite as it's expensive (an activity themed event). I said he can invited a few from school and few from outside of school.
Handed out invites at school discreetly to parents today but the kids involved where running up asking "is so and so also invited?" "he's in out group" and similar questions. Where do you draw the line? I had to be strict on number for financial reasons but obviously kids so young don't always understand that :( Feel guilty about the friends he couldn't invite.