Swapped pedal onto new bike (18" wheels, not 20" as at first thought),
adjusted saddle and persuaded #2 to go to the park.
He has been a reluctant learner, being of the school that likes to work
things out in theory and then just have them happen - hasn't yet sussed
the difference between theory and practice [1]. I'd promised him a new
bell for the bike when he could ride 10m unaided (ie after he is up to
speed and I let go, he has to ride 10m in good order). With the new
bike = bigger wheels = a bit easier to balance, he was well away. And
thoroughly enjoying himself. Able to bring himself to a controlled stop
too.
So one very pleased boy, and when we got home his Dennis the Menace
bell got fitted.
...d
[1] greater in practice than in theory.