So, you assume that “No gifts” on an invitation really doesn’t mean much, as most people feel compelled to bring a birthday gift for your kid. So, you know the one gift that your kid really wants, perhaps an expensive video game or special doll. Something that costs money, and a gift card to the store would really help you purchase that special gift. How can you state this on the invitation?
Telling your guests specifically what your kids want as a present actually makes it easier on people, although it can seem to some that you are making assumptions about the gift part of the party, and kids should just be happy with what they get. Still, without mentioning an amount and/or mentioning a small amount of money, i.e. $5, it is perfectly reasonable to ask for a gift card to put toward this special gift.