In Europe they use a variation of the popular "trail-a-bike". It allows the youngster's bike to be towed behind their parent's bike. When it is safe for the kid to ride, they are "unhitched", and can ride their own bike. The hitch flips up onto the parent's rear rack.
They are also started young.
However, some young folks need a little help with pannier organization. This young man was carrying all of his own things.