Louis for your response.
Those of us who have taught children's classes experience a different level of frustration on occasion (not to mention joy) which we do not necessarily have with the adults.
The reason for an age 6 bottom limit for me is the child's skeletal development. Quite often in younger children the collar bone is not as sturdy as we need in the rolls, and they are subject to "green stick" fractures.
We must grow them larger in St Louis, because I have been finding 11 year olds at 5'1"+ and 100+ pounds which puts them over the smaller women in my classes.
I have had the experience with parents you have mentioned. Basically, I give a lecture when the parent enrols their child that while the child is on the mats, their behavior is my concern. However, since I began to teach children back when the McMartin Pre-School molestation scandal was breaking, I have always made it my policy to have the parents in attendance. My other reason is to keep them involved in their child's training and not to use Aikido as a cheap baby sitting situation by dropping the child off and leaving. I have found the occasional parent's "correcting" from the side lines to be worth the sacrifice.
I look forward to hearing from you and others.