When my children were 7 or 8 years old, I had them in Aikido, and the instructor, who has since deceased, taught my children basic gooseneck wrist locks, and throws or moves ustilizing the elementary wrist locks. My children have grown up without any ill effects on their wrists, elbows or shoulder joints.
I wonder if you know of senior students or colleagues of your kids' instructor? That could be a good resource. Perhaps you could get some of them interested in your ideas (if I'm understanding right, to get a few aspects of Aikido taught in Karate schools?)