I am another voice against wrist locks on kids - in kids aikido classes it is what we DON'T do because of the growth plates and other issues. Teaching kids to move off the line, evade, block a punch, yell NO, fall without getting hurt, as well as the discipline of lining up, bowing, etc is all much more valuable then any locks or techniques.
Because Wrist Locks are a tool that can be used with too much force and cause injury, means that teaching wrist-locks carries with it the idea that it is good to take extra care in teaching kids the dangers of too sudden, or too forceful wrist locks.
It is possible that I will conclude that it is not possible to responsibly teach sub-teens wrist locks. For now, I am looking for ways to increase responsibility in teaching, and looking for specific problems with teaching wrist-locks.