It is actualy illegal for anyone to cycle on the pavement no matter what age. In cases of children (and acompanying adults) the police are to use there discression.
this is what I found so far;
http://www.rjw.co.uk/ctc/q-a-from-cycle-magazine/q-a-from-cycle-magazine#pavement2
@edscoble started
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this is what I found so far;
http://www.rjw.co.uk/ctc/q-a-from-cycle-magazine/q-a-from-cycle-magazine#pavement2