All the credits go on all the cards; if there are four of you on your reservation, for each night of that reservation your card will have four table service credits, four counter service credits and four snack credits; your spouse's card with have the same four table service credits, four counter service credits and four snack credits; and each of your children's cards will have the same four table service credits, four counter service credits and four snack credits. If you're there for four nights, that's sixteen of each credit on each card - so you need to make it absolutely clear that the credits need to last for the entire trip, and probably specify where your kids can eat while they're apart from you, etc.