When to start?
The main difficulty for very young kids is having the strength to hold the bike upright when stationary. Around the age of two (some earlier, some later) seems to be about right.
Most of us learnt to ride with stabilisers. This really does hamper the process of learning to ride. Balance bikes are the way to go. There are loads on the market now. It’s worth getting one with a brake. They get fast really quick, and it’s good to learn to use a brake early to save on shoe soles in the long run. Islabikes and Frog bikes are great!
Counterintuitively, setting the saddle reasonably high to begin with can help with balance, but putting it down lower will help get a really good stride in for speed.
This choice is less obvious. Has your child really taken to it like a duck to water and all they need now is more speed and a bike that won’t hold back their desire to push the envelope of what their parents can bear to watch them do on a bike? If so, you need to get them a micro-mini BMX. These can be really versatile; not just for the BMX track, you can put the saddle up for MTB rides, or even pimp them into a cyclocross/road bike.
[Above] Haro micro-mini BMX with drop handlebar modification (doesn’t do much for the handling, but he loved it).
If your child prefers to potter around and something a bit more stable would be more appropriate, go for the next size up Islabike, Frog, or equivalent (our kids did this before moving to a BMX).
At this stage I recommend you stay away from gears and any form of suspension. You might want to consider going for one of the bike exchange schemes that are starting to appear, where you pay a monthly fee and get to exchange the bike for a larger one when the time comes.
Bike #3 and onwards
As your child gets bigger, the temptation to go for gears, suspension and disk brakes gets greater. Hold on for as long as you can, unless you are prepared to spend a lot of money. Weight is a more important factor at this stage.
Once they’re over the 135cm mark, maybe you’ve got an ageing mountain bike you could salvage some better quality parts from for them? You could buy a small 26″ wheel carbon frame online from China and put your parts on it. This might make buying a whole new bike for yourself seem more reasonable.
These can go really badly! I get annoyed when adults get punctures or need to make adjustments on training rides, so I am terrible at being on a bike with a dithering child, who is completely unable to project into the future to the warm fire, tea and cake, and so see the benefits of getting a move on. Even if you are a saint, the best option for a family bike ride with young kids is to have at least one grown up running to field the way fallers. Singletrack have a good article on getting your kids to enjoy riding.
BMX is a fantastic way to improve skills. Many tracks run balance bike sessions and races. Age categories then start at six-and-under, and go up one year at a time. This means your child is only competing against children their own age rather than six year olds being trounced or overwhelmed by huge 11 year olds in an under 12 cyclocross race.
The best thing about BMX though is what a friendly community it is; all the kids share advice, pick each other up off the dirt, etc. While tracks tend to be open for public use most of the time, it’s best to get in touch with your local club that runs the track to find out when they have appropriate coaching sessions for your child’s age. You will probably be able to borrow a bike and helmet. Make sure your child is wearing long trousers, sleeves and long-fingered gloves.
This is a great cycling discipline for families. We have a whole book dedicated to it!