I took mine out when their legs were long enough for them to be able to sit and
have their feet rest on the passenger pegs. On a CL 175. Trail riding earlier than that. That got them interested. They were
a little apprehensive about the street the first time. I'll never forget my daughter's
reaction once as we crossed the Missouri river bridge. She never said anything, but her body language sure did. She was maybe in the fifth grade. After a few rides, she got
into it..Faster Dad, Faster!
...On a serious note, ALWAYS err on the side of safety.
Make sure they're dressed well with the appropriate safety equipment, and avoid routes with a lot of traffic. We didn't do it a lot, but both son and daughter knew
what to do/how to act. We were never in a hurry, just enjoyed the ride.