My preferred system for carrying a young kids is the Child's Riding Belt (formerly the CRV Belt) ($129) from Child's Riding Belt Company, and imported by several retailers for the U.S. market. The CRV is a harness that goes around the child's waist, over the shoulders and between the legs so she can't wriggle or pull out. The quick-release buckles are all on the back so she can't release them, but getting in (before the helmet is donned) is quick. The child's harness fastens to a foam-rubber pad with handlebar-type grips. A large belt, attached to the front of the pad, goes around the rider's waist to secure the child to you. The child cannot fall off unless you do. My kids routinely fall asleep back there, and we have even ridden off-road, jumping and bouncing around, with no fear of them getting thrown off. Of course, if you did crash, the child would be attached to you, which might cause additional injury if they ended up between you and whatever you bounced against. On the other hand, you can also jump up to leap out of harm's way, and the child, since it is attached, will come with you, without the need for an explanation.