Two nights ago the kids and I watched Dirt! The Movie together, and I loved the message. In all the known universe, only our planet has a living skin, called Dirt.
Kids love to play in the dirt, and my children were very interested in this portrayal of the aliveness of our dirt, the dangers to it, and what we can all do to love the dirt. The middle of the film, which portrayed strip mining and many other environmental problems, was a bit too intense and sad for the kids, but we stuck with it and the film-makers did bring it back to a positive message of change, so the kids were OK. It's such a fine line between too much scary destruction just leading to despair and too little attention paid to problems maintaining ignorance and the status quo.
Some other films we've watched as a family:
No Impact Man, but this one was a bit boring for my kids. It would be good for middle school and up, I think.
Planet Earth, of course.
The Blue Planet is a David Attenborough look at the watery parts of our planet.
Food, Inc. was a bit too much for the kids, again, but it was a hit with the youth group at church.
The Life of Birds - we love David Attenborough!
Life in the Undergrowth - David Attenborough again (but this one featured slug sex, which has to be one of the weirdest things we've ever watched as a family)