Most kids pick up pretty rocks at the beach. Sometimes this leads to a life-long interest in rocks, rock hunting, and rock collecting.
Rockhounding New England: A Guide to 100 of the Region's Best Rockhounding Sites by Peter Cristofono [552.0974 CRI] is a guide book that takes you to locations, including some in New Hampshire, where you can look for rocks. Most quarries and locations, however, have restricted access.
There are museums in NH that are open to the public that have collections of rocks and minerals for viewing. The Little Nature Museum in Warner, and the Woodman Institute Museum in Dover are two. Really close to home is America's Stonehenge in Salem, which is having a "Kids' Gemstone Dig" until Labor Day.
An online gallery of NH minerals can be found here. And for those wanting to learn more about NH's rocks and minerals, the NH Geological Survey website might be the place to start.
Back to those kids who may want pursue their interests in rocks: I was recently told about a page for Rock Hound Kids that has lots of links to explore. (Many thanks to the kids of Colonial Academy for their suggestion.)
Here are some books and DVDs from the Library's collection: