I should have realised that Phil would have something about moons somewhere on the site. Doh!.

Thanks for the suggestions, they've given us some good ideas to pursue.

In the age of the internet, I sometimes find that when my kids are given a broad subject like "space", it's difficult for them to narrow it down into a specific sub-topic they want to research and to further refine the enormous amount of data out there into something relatively concise but also informative and interesting.