Have LO make a little something (I just did an easy art project with my kids to throw in with our gifts to the grandparents - I painted their feet and made their prints look like Christmas trees with lights and a star on top of each one). Throw in a gift card for some major chain store or restaurant along with it.
In my former life I taught elementary school and while I know it's not the same as a daycare, I would have totally felt weird getting cash from a parent. Homemade gifts were always my favorite ;)