Personally, I don't think he'll need to know specifics from the movie Avatar in order to enjoy the land of Pandora. You might look at the various videos available online and tell him that Pandora is a planet far away in space, that many years ago a mining company did a lot of damage to the ecology and environment of the planet, and that now the damage is being repaired and people are beginning to appreciate how beautiful the different plants and animals and scenery are there and that the customs of the native people should be preserved. It seems that my 8 year old DGD is aware of ecology and environmental issues on Earth, so hopefully he is too, and I think that's the message of Pandora (and all of AK, for that matter). It's also like visiting different places on Earth, like the rain forests or the mountains. Some things look similar to what we have here, some things are very unique.