I would think it would make him wiggle side to side more and maybe off the chair. What about some kind of triangle cushion to force him to lean back? Or if there are settings on the chair that lean the seat portion back?

Before I make the purchase, anyone can tell me if that will help a small kid to sit back at an adult sized office chair if I place a wiggle cushion to the back. Small kid watches YouTube videos at desktop computer, and he fell off from office chair or slide down office chair because he sits too close to the edge.