When our kids started riding pilion, they were aged 6 and 8. I bought them a Child's Riding Harness. I got it on the internet. I think it came from Canada. It straps round the child's waist and shoulders and the tops of their legs, like a parachute harness. It's very secure. Then there is a thick belt which goes round the rider's waist and secures the child to the rider. It worked really well. When our daughter was 6, she would fall asleep while riding pilion. She would flop to the side, but was held in place by the harness. Now they are a bit older, I use Love Handles, one of those belts with handles on the side for the pilion passenger to hold on to.