Interesting feedback on the Adam's trail-a-bike. My husband has been using one with our daughter since she was 4.5 years old and he's never had any issues. Of course, at six years old now she only weighs 39 lbs. so there's not much weight for her to throw around back there. I would agree that they definitely have to be trustworthy enough to hold on and I would say that my almost four year old son is a long way off from being able to use the trail-a-bike. He's just too impulsive to be trusted, so as he outgrows his bike seat, I'm looking into getting a trailer for him.