Personally I'd be against my kids learning any moves that could be fatal with application. Locks I'd be less concerned about and I think they are part of the Judo syllabus.|
I think my chief concern with little-uns learning MMA is that there's no natural progression gauge other than competition. At least with the traditional arts, there is the natural motivation of gradings and belts and no pressure to compete.
When you can't see the angles on the wall you're in trouble.