Yep, quad bikes (4 wheelers) are so easy to flip. Far more dangerous than a normal bike.

My DD has been on my DH's bike for... gee, just about as long as I can remember. I know to start with she didn't like the noise when she was very little - 1-3 maybe, but since she was 3.5-ish she used to ride around the court we live in infront of DH between him and the tank. This is the safest spot for little 'treat' rides.

Since she was about 7 or 8 she has been out with DH on the road. She wears a proper helmet, jacket, boots, gloves - the works. Yes I still worry but it's in the family blood - she was bound to want to be on the bike. She's even done the MRA Toy Run - on DH's bike from the city to Williamstown over the Bolte and Westgate Bridges - she had a ball amongst the 100's of riders.

And yes, she has been on the bike when it's gone down - fallen/hit the ground. Fortunately it was up at our local shopping centre and the bike was stationary and some loser wasn't looking. Neither DH nor DD were hurt but it did give her a fright. She still, however enjoys going on the bike, and knows the risks, as do we.