[yeppers8]

Unity seems a bit tricky for a 9 year old even with this update, you might want to check out something a bit simpler like Construct 2 to start with. Just an idea

[300bps]

Checked it out - looks awesome and will be downloading the free version to try it out first. Anyone else have other suggestions?

[pajaroide]

I prefer Gamemaker Studio (http://yoyogames.com/) it's more code oriented but very easy to use. There's a free version too. Look up Hotline Miami if you want to see a commercial game made with it.