Have your child make a scrapbook, either alone or with friends. It could include drawings, notes, cut-out pictures and photographs--anything to remind the driver of the children.
There are several websites with gifts for school bus drivers. There, you can buy t-shirts, ties and other apparel with amusing and appropriate sayings.
Help your child bake some simple cookies. You can buy school bus-shaped cookie cutters and frost the cookies yellow.
Several sites enable the printing of personalized items. Have a mug printed with the driver's name and school. Fill it with candy (Hershey's Kisses work well).
Sewing samplers, hand-made cards, collages, drawings and models are all appropriate gifts. If the craft can be personalized, better still.
Appropriate gifts include photo frames, gift certificates, music CDs, chocolates or cookies. A bus driver might also appreciate a warm hat or gloves.