+1 on Ford Museum. Also Crossroads Village in Flint is cool. Just don't drink the water.
http://www.geneseecountyparks.org/crvdefault.asp
Now for the real fun:
Since I used to live in Michigan and he is Korean, I would suggest for non-family activities, The Wild Mustang, BTs, the Silver Cricket on MI Ave, then cross the bridge and hit Jason's, Million $ Club. Bring lots of $1s and $20s