I'm now a grandmother, but have 4 grown children and 3 grandchildren. I had a home-based child-care business, until my mother became ill and we moved her in with us so I could care for her.
You're fortunate that your son enjoys his teachers...and so is he! Some of the best gifts I received as a child-care giver were tickets to movie theaters, gift certificates to restaurants, Dairy Queen gift certificates, a massage from a local massage school (inexpensive), a gift certificate for a haircut from my favorite hairdresser and some cozy slippers. If any of the teachers have little ones of their own, maybe you could offer to babysit for them on one of their days off, so they could have a little time to pamper themselves.
By far, my favorite gifts were seeing those little ones coming to my door every day and helping ME to be a happier person! I loved those days and am considering doing childcare, again, as Mom passed a couple of years ago.
Wishing you and your son a wonderful Holiday Season!