http://www.childridingbelt.com/engprod.htm
I've also found belts that have handgrips on them, but they are totally dependent on the hand strength of the person (or kid) holding on. The harness above is not. The only way the passenger comes off is if the driver comes off. Anyway, that's in the future. Along with helmet, gloves and a leather jacket.
Peaches has been riding with me since she was old enough to ask to ride...first on the Harley (in the front) and now on the Z. We only ride through the neighborhood, and rarely get above 15-20 mph. We did have a dog chase us one day, but he was slow and we were not :-)
She loves going fast. We've ridden jet skis and all she wanted to do was go faster and faster. I had the dang thing up to 50 before she decided that all that wind in her eyes was enough! When I had the El Camino she would sit in the seat with her head out the window, wind blowing her hair back and her eyes closed just feeling the air moving. Sure we were just tooling around the neighborhood, but she liked the feeling.
I've got a buddy who's got a 22' boat, and she likes to ride in the front as we motor on. This ain't no cheesy pontoon boat either, he takes it off-shore for fishing.
Maybe one day she'll get a contract with NASCAR and I can retire to a life of luxury....
What do you do with a 5 year old when it is 65 degrees outside in January? Go for a ride on the bike! Peaches thinks she has the coolest dad ever. 
