Thanks for the tips Bruce. The Fuji Absolute bikes look sharp
http://www.fujibikes.com/bike/details/absolute-24 and appear to have decent components. They have dual pivot road brakes though, so I wonder how wide of a tire they can fit. Specialized Hotrocks are more mountain, and nice that they give you the option of a rigid fork. The rigid fork 24 inch has a triple though which I think is overkill for a kids but but I could always swap it out or take a chainring off.
I have some ancient but nice older 6 and 7-speed XT level stuff lying around (hubs, thumbies, canti brakes). If I really wanted to go wild I could build up a bike, but probably not worth the effort unless I just want a project. Have to find a nice frame... Maybe my older son could help...