We got my little son a balance bike without pedals. His buddy had a regular bike with training wheels. They traded back and forth naturally all day and learned both components in near-isolation. Putting them together came very quickly.
(We still used the balance bike long after he could ride a regular bike because it was so much lighter to carry and had no greasy chain to get on clothes and car seats.)
(We still used the balance bike long after he could ride a regular bike because it was so much lighter to carry and had no greasy chain to get on clothes and car seats.)