A Trip to the Moon is a very simple short form RPG. It borders on being a GM free system, although one player will play the moon and that borders on being the game master in some ways. It is also a very sweet game with one of its guiding principles being that you should treat each other well.
In A Trip to the Moon, almost all the players will play children who are somehow magically visiting the moon. The one person who doesn't play a child is going to play the moon itself. The ultimate goal of the game is to tell the kind of bedtime story that will help a child go to sleep and have sweet dreams.
While each stage of the game has a different set of rules, there are three rules that always apply. Always listen to each other. Accept with the other people have to say and work with it. Always create something that a child would like to hear.
At the start of the game, you dim the lights and everyone sits down on a pillow and snuggles up in a blanket. The game is entirely spent as a conversation, with everyone having a turn to speak. You will use something like a tennis ball or other token so you know whose turn it is to speak. You should use simple, clear sentences with one idea.
The game gently progresses in stages. The players create children and choose which children they will play. They describe how they go up to the moon and then the moon will interact with them. When the children grow sleepy, the moon will send them home where they can go to bed.
I have looked at a lot of games that don't require game masters and play with storytelling and push the limits of what you can do with role-playing. In many ways, A Trip to the Moon succeeds in doing all of that but by going in the opposite direction then I am used to.
Honestly, I think the biggest hurdle a group will have with this game is that there is not only no conflict, but an active requirement to be nice to each other.
I have also looked at a lot of games with an eye for playing them with children, ignoring the fact that my son will probably only be interested in baseball. While the goal of A Trip to the Moon is to have adults embrace being childlike, I think it would work well with real children.
Part of what makes the game so accessible to my mind is that, despite the amount of free-form it allows, it also has a very tight structure. There are distinct stages that you go through as you play the game. I think that would make it work well with people not used to role-playing games, as well as children.
A Trip to the Moon is a game defies most of what I expect in an indie game and it's even out of the Nordic School. But it's one that I think would be a really good one to play. It's a game about creating a safe environment and I haven't seen many like that.