I order travel mugs from oriental trading that you can put an insert in. They are about 3.00. Then I take a picure of the class and at the bottom, I print Thanks for all your help this year! The moms loved it last year so we are doing it this year too.
One year I did measuring cups (the large ones-plastic) and I filled them with tissue paper and candy. On a tag I typed "Great Volunteers Really Measure Up!" I attached it to the handle with curly ribbon. They were really cute.
This seems to be my standard answer...but they can always be used. A nice attractive frame makes for a great present. You could even take a digital photo of their child and place it in the frame. Or perhaps the class? Look at Target or Wal-Mart.
Hope this might help.