Documenting the summer with a photo challenge—who's doing this?

We're trying something new: every weekend the kids pick a photo theme (like 'something wet' or 'your best friend' or 'funny faces') and we all take pictures. Then we vote on the best one. My 9yo is actually getting interested in composition instead of just taking 400 blurry photos of the dog. Costs nothing, keeps them busy, and we're building a fun memory book. Anyone else doing something like this or am I reinventing the wheel here?