We have Disney Infinity 2.0, the Marvel one, for my DS, he's 5. It's great fun. You can buy a starter pack for Disney Infinity, 2.0 and 3.0 (which is mainly the new Star Wars one I think?) which includes the software (disc), the base, and a game pack. The figures are sold separately and there are loads to choose from.
The game pack has 2 figures and a crystal type thing in the pack. You need the crystal on the base to start the game, then you add the figures onto the base. When you put a figure on the base, that character magically appears on the screen and you get to play it. You can change/add figures as often as you like. It is ideal for young children.
Only thing is it can be complicated to understand - there are power discs which can be used; you can only use certain characters with certain game packs - ie you couldn't use an Aladdin figure in the Spiderman game.
We've had it a while and still can't get my head around it! Buy DS loves it - he can play as any Marvel character (as long as we physically have the figure) and go around beating up baddies, solving puzzles, collecting things, and it's not too difficult to control either.
Your best bet is to go into YouTube and have a look through some of the Disney Infinity videos on there. Also if you go into a Game store, their staff there will be able to help too.
It does sound confusing but very easy to use for a 5 year old just wanting to play about.
Hope that helps, sorry if I've confused you even more! 