Do you have a budding scientist? There are a lot of reasons why Ecospheres are such a cool product for kids.
If you live in a no-pets building, this might be the answer, especially if you aren't up to caring for a whole tank of fish. But also, on a more serious level, if we want our children to understand why taking care of our environment is so important, maybe the first step is to show them how an ecosystem really works, on a scale that makes sense to them.
Ecospheres were developed by NASA, and are complete, closed bio-regenerative ecological systems, sealed in hand blown glass. All you need is indirect sunlight, and the algae, shrimp, and microbes inclosed within will sustain each other, and themselves. 4" sphere, or 5 1/4" pod, $59.99.