Got to be a bit careful what I say here...
Not so long ago, in a galaxy not so far away, I was following a bike with a child on the back - broadly similar age. At one point the child's feet came off the pegs (both) and waved about a bit before resuming their normal position.
No problem with the riding, the child was just having a stretch or whatever.
As I watched I was concerned about feet meeting spokes.
A later look indicated that this was rather unlikely.
Having read this thread I would have thought the feet were even more unlikely to meet the bottom chain run. Perhaps a smaller bike, or a bigger kid may alter the risk factor.
There is a grey blur, and a green blur. I try to stay on the grey one. - Joey Dunlop
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