I think a 7-08 is surely enoug gun for sub 100 shooting. If the kid can shoot it, I would not hesiate to use it. I've personally seen people sucessfully use a 30-30, .243, and a lever 44mag rifle for bears. The 7-08 appears better than all of those guns for black bears (IMO).
Just an idea if you're shooting short yardage: My 12 year old daughter is using a 20 gauge single shot youth model for baited bears this year. I had the barrel shortened to 18.5 inches (so we can still take to Canada) and drilled and tapped it for for a Weaver style rail. I put a small off-brand electronic site on it because the rail is really short. It shoots really well at 75 yards with the cheapest factory 3/4 oz. Winchester slugs I could find to sight it in (for a short barrelled no choke smoothbore). 4.5-6 inch groups 3 times in a row from a bench. I haven't shot it past that distance because I can't imagine a shot over 25 yards where we hunt over bait and I only had 15 rounds to work with that day. Maybe I'll try a 100 yards just for fun when I get it back and put it together.
The gun is really, really light. The short hollow plastic stock feels more like a toy, but its perfect gun for her. I'm having it cerakoted and the stock and forearm hydro dipped in the pattern she picked out. She's excited, and I am too (to have her take a bear with it). She's a girly girl and I'm trying to keep her excited about going hunting... hence letting her pick the pattern for the stock... This gun is now so short and light, it might start having it accompanying me on backcountry trips. The only thing I'll do is swap out the electronic site for a "See-All" sight on the same rail. Sorry if I am derailing your topic... back to the topic at hand.
The guy who said that they can cover some ground after the shot is spot on. Their long hair can clog up the wound opening real quick too. I like big holes for a big blood trail. That's the biggest reason I chose the 20 gauge for my daughter. We have a better chance at recovery if she makes a poor shot.