1. How old were they when you let them ride with you on the street?
She was 6, but IMHO age is secondary to emotional readiness and being physically big enough to fit safely.
2. What do you do to help keep them safe (gear, kiddie riding belt, etc.)?
When we first started out, I wore one of the belts with handles for her to hold on to, but we've since retired it. One of the main things we do is every few minutes I tap her leg, she is to immediately tap me on the back. If she doesn't respond to an immediate tapping, I know she's not paying attention or napping, and it's time to pull over.
3. Where did you get any kid-sized gear?
Living in the 4th largest metro area in the nation has SOME advantages. Went to a few different motorcycle shops and found appropriate gear for her. Mommy is VERY insistent on ATGATT for the kiddo, and I'm not gonna argue (Long pants, gloves, jacket, helmet being primary)
4. Do you enjoy riding with them, or are you in such over-protective mode that it's not even fun to ride with them?
At first I was extremely paranoid, but as the miles have gone on (We've done a few thousand together, longest trip is up to about 60 miles between stops thus far) it's become more and more rewarding and less paranoia. Definitely worth it, and we both love the time we get together on the bike...
One other thing, I make a bit of a big deal about ALWAYS asking permission before getting on OR off ANY motorcycle, and also emphasize - If it's shiny, don't touch it, it's HOT.
