T.N.
Involving your kids in some kind of craft or card is great. It teaches them to show appreciation to others. Adding something to it, such as a gift card, makes it more usefull. If time is to pressed for the craft, you could include your child by letting them pick. Bath & Body works is a great place for this because you almost can't go wrong.
I have found that smaller gifts, that you can give more often, are really better. It keeps them from feeling guilty, like they can't accept the gift. It also praises them for the great job they do with you child, more often.