HeroScape is pretty good -- not a really great battle sim if you have ever been into that, but a pretty fun game based on that sort of thing.
I play with my 7-year-old. Once kids can read and do simple math and are mature enough to realize you can't go around slashing people in real life, they can play. There are actually 2 versions -- each character card has 2 sides -- one is really simple and very random like a board game, the other gives the characters special abilities and makes player skill more important.
The included scenarios are OK, but it is a lot more fun to make your own battlefield and create scenarios for yourselves.
A lot of expansions are available, and the sets make the game more fun.
It also takes a while to create the battlefield, but nothing like making it out of hex paper.
We typically leave it up for days at atime and make minor changes if we are going to play.
We usually end up getting into it around the holidays, since my son generally gets an expansion set or 2 as gifts, and these are a great time killer when family is over.
Be excellent to each other.