L.T.
If the others that work at the center work directly with your son (aide, co-teacher, etc) I would try to find a way to afford a gift for them as well. If you would like to consider alternatives, how about gift cards in lesser denominations, cookie/snack/breakfast tray to be shared or Christmas ornaments? Some teachers appreciate things for the classroom such as art supplies, books or subscriptions to teacher/caregiver magazines or children's magazines (they have ones for infants/toddlers that are more like board boooks).