Who comments about this? If this is a dck, do the parents know he has no appetite in the morning? or did he eat at home before coming to you?
If this is your own child, then what you do is just fine. You know your kid best so as long as he eats shortly afterwards, at snack, then he should be fine.
I would say dont bother nagging, it will just be more stressful on you and he still probably wont budge anyways.