This might be a callus approach, but remember that one bad apple can spoil the basket. Your team is much better off if you let him go, especially if then goes and joins an opponents team. Otherwise, you will have to put up with other teams bad-mouthing your team and kids for several seasons to come regardless of how they do. By the way, I think most older youth league coaches, at least those around here, have learned this lesson already. Another problem associated with running a kids practice is keeping them focused and under control.
Kids have a very short concentration span compared to high school and older age groups.
For this reason, practicing the same move over and over, or showing the same move too often will create serious distractions. The kids who know it will start to play around and the kids who don't will follow right along rather than learn. To keep their attention, show three or four moves, at least one complex enough that no one will learn it first time. Show the moves, spend only a few minutes on each, then go to some other related activity like getting into the move and then live wrestle out. After about 5 minutes you can go show the move again followed by a second live session.