I think it might be fun to make some rings and charms.
This great tutorial at PlanetJune for fun and simple Shrink Plastic Rings is great inspiration.
If you decide to do this, there are some good tips in the comments and it would probably be a good idea to check with the other mothers about working with hot materials.
Then there is this tutorial by Meander on the ThreadBanger Forum about glazing shrink plastic charms with clear embossing powder. It's a nice soft finishing touch.From Ruby's Jewelry Design and Beadwork is this simple beaded ring tutorial.
Ruby has quite a large collection of beadwork tutorials here.
This printable ring sizer from AtlantisRing.com would be helpful. You would want to have the correct size mandrels (dowels, pens etc.) for each girl to wrap her shrink plastic ring to the correct size.