I have been told by ATF that letting someone use one of my NFA items is not considered a transfer so long as I am at the range. I shoot the Florida Subgun match every month and asked ATF if someone could use one of my subguns and shoot on a different squad. So I would be on one bay and they would be on another bay. ATF told me as long as I did not leave the clubs property it would not be a problem.
I do let the kids shoot the 22 LR full autos at the range if they want and there parents say its OK. There is nothing better then the smile on a kids face when they get to shoot a full auto.