Party Ettiquette

[EmsMom]

So today was ds's bday party. One of his friends showed up but didn't want to stay. Both his parents tried convincing him but no dice. So after about 20 min in the foyer of the venue they left. Should I have sent their present with them? I feel bad they had to buy a gift and not get to at least enjoy the party! This is not an isolated event btw, their son often doesn't want them to leave him at school, friends houses etc so I suppose they must expect it to some degree. DS opened the gift before I even realized it was from the child that left. Should I do or say anything? I'll be sending his goody bag to school on Monday.