Finding other ways for children to take their experience home is an opportunity to teach kids about the value of the data rather over personal possession of the artifacts.  Perhaps they could draw or take photos of their finds.  Given all the issues we have around pothunting and the messages that come out of television shows such as Diggers, I think allowing kids to take artifacts home sends the wrong message about archaeology.  I have elementary school-age kids myself and I know that though they would love to have their own arrowhead or some other special artifact, they don't need them to enjoy the experience.

Good luck with your project!
Hannah Ballard