Fear of doing tricks is a difficult thing to tackle, but bunny hops should be pretty easy to overcome. He's probably concerned about the wheels slipping out to the side. Have him practice dropping off curbs, off boxes or ledges, or anything else taller than 3 inches. Once he gets used to the impact of the drop and learns to land and stabilize himself on the scooter, he should feel more comfortable going bigger. I hope that helps. Good luck!