Hi guys

It's my sons birthday coming up and he's interested in picking up an RPG. We play Warhammer Quest a lot and he is looking to get into something less... mechanical and more flexible. I'm also hoping to get his mum involved as as close as they are she really misses out on the whole wargaming / fantasy side of the little guy.
Now I've never played a proper RPG, ever. My gaming group has always been so small that requiring a DM has always hindered us picking these up. I'm more than happy to DM for the missus and the lad but really need some advice about which one to get or look into that would be suitable for a 7 year old (he's a bright lad though and good with rules...)
The things I'm looking for are something very flexible, something with quite a bit of combat possible (he's STILL a 7 year old boy!), something with quite tangible increases in power or levels and something that my other half can get involved in without it all being just dice rolled...

Is D&D the way to go? He loves Star wars too, is that any good? What about the Warhammer one, he's keep on the warhammer world...?

Any advice would be greatly appreciated!