I'd be careful going by breeds. TB's do tend to be hotter than QH's, but it's definitely inconsistent. I've ridden QH's that won't stop cantering until you practically run them into a wall, and TB's that won't move.
Each horse has an individual personality. While looking at Paints, QH's, Morgans, etc. is a good starting place, you have to be sure and evaluate each horse seperately.
That said, I'd also consider some pony crosses, draft crosses, etc. as they tend to be a bit bigger or smaller than their purebred counterparts, respectively. And the pony/draft blood will often make them a bit calmer than other horses. Still, evaluate individually, because you never know...
Good luck to you and your friends!