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Twice in one day actually.
He and I did a little riding yesterday in the park next to my house. It has been a couple of months since he rode, so he needed to remember how to do everything. Since he is not tall enough to put a foot on the ground while sitting on the CRF 50, the bike has training wheels. I was following him on the TTR. First as we were heading to the park, he crashed into the fence because he forgot how to stop. He was ok though, he had everything on.
We then rode around for about an hour or so. Some times I would follow him, some times he would follow me. Well, he took a left hand corner a little too fast, and rolled the bike over. I thought that this was going to be a breaking point and that he would be afraid to continue riding, but when I got to him and checked, he had a big smile on his face. I got the bike back on it's wheels, and we rode for about another half hour. My wife took him and my daughter out on the bikes later in the day.
He took the crash really well.