Geology is a favorite subject of my kids. They love learning about different types of rocks, and have some pretty good collections for their ages. One of the really great parts, however, is how easy it is to introduce kids to geology.
1. Notice the Geology Around You
The very first thing you can do with your kids doesn't take any money. Just notice the geology of the area around you. You can point out layers of rock in canyons or mountains. You can pick up rocks that you find and learn about what kind of rocks are in your area. There are a number of websites out there which can help you identify rocks and minerals. We've found some nice plagioclase feldspar in our area, for example.
You can also make a point of looking at the geology of any places you visit. If you're going on a family trip, make sure you point out how the land changes as you go. The changes don't have to be dramatic, although it's certainly fun to be able to point out the cone of a volcano or a truly impressive rock formation.