Wow! It's a blessing that you've posted it here right now! I am heading into the same situation exactly. How did you teach your kid to ride without the training wheels? Did you use any knee protection or helmet, or anything? My daughter is 5 years and 5 months old and she has to adapt to riding her 16"-wheels bike without those helpers next weekend. Are you asking, why so immediately?

That because the left one has broken... I guess it's a great opportunity for a change...
Good timing indeed. Actually I had the same situation exactly - broken left training wheel. Spooky.
He has a helmet but no knee or elbow protection. My both my kids (the other is 3 years 5 months) have always worn bike helmets since they started riding, even with training wheels - it is the law here. My sons bike is a 12".
This is a bit wordy, but you did ask

. Like any true engineer, I had solid plan worked out in my head beforehand. Before starting we sat with the bike and explained the basic concepts of bike riding:
1. Keep the bike up straight.
2. If the bike leans, turn into the lean to get the bike back up straight. Use small fast steering inputs for that instead of large slower ones.
3. For turns, use slower steering inputs and lean into the turn.
4. Keep pedalling to keep your momentum up.
My strategy was to simply run alongside the bike loosely gripping the back of the seat (that way you can avoid the worst of the falls) and calling out instructions. On occasion I would also put my other hand on the near side handle bar to give him a feel for the steering inputs required. As his competence increased I would ease off my grip on the seat to the point of letting go, but keeping my hand nearby in case I needed to catch it again.
The biggest barrier to success was keeping his confidence up so that he would keep pedalling (each fall was like two steps forward and one step backwards) so plenty of encouragement and praise for small successes was required. In that regard, I also suggest going somewhere where other kids are riding without training wheels - it will give her confidence that she can do it herself. Also, keep your practice sessions short (we would go for about 1 to 1.5 hours, with a 15 min break in the middle) so that her legs do not tire too much. Other than that, keep up your patience and repeat, repeat and repeat some more. Good luck
