Check out our online Teacher's Guide to Caves and Groundwater, "More Than Skin Deep." This contains information, classroom activities and hand-outs, generally suitable for grades K-8 or homeschoolers. Teachers or homeschoolers may also request a print version by contacting us.
There are lots of great websites out there as well. This link is to one of the best listings of Environmental websites for kids. The links are all high quality, fairly unbiased, with many official US and Canadian government agency kids' sites. You'll surely find something useful here.