The Great Falls Discovery Center is a nicely kept little nature center, near the fish ladder and Unity Park, a decent playground with the only real see saw I've seen recently. I parked on the street, for free, right outside the Center. There is a cute little garden outside and well maintained yards, but this isn't really outdoor space for the kids to play.
The interior boasts many dioramas of local animal life, including several interactive features (buttons to push, a computer program to play with). However, for my 5 year old, the displays were quickly digested (especially because he has seen quite a lot of these kinds of exhibits). The most engaging area for the kids was a small table set up near the gift shop that held tadpole-to-frog models and books on the same subject. There are quite a few activities held there for the preschool set, though I haven't attended any yet.
The whole museum was clean, including the restrooms.
After exploring the Discovery Center we made our way to Unity Park, down the street. What appeared at first glance to be dilapidated turned out to be a pretty nice park! The equipment was a good mix of new and old, a pavilion provided shade for our snack, and the sport fields were in use, creating a nice community feel.