Guide to Kid Bike Sizes: Children's bike sizes are determined by wheel diameter, not seat height and frame size as is the case with adult bicycles. The chart below should help you narrow your search, but it is not a substitute for an expert helping you find a bike that is most suitable.  A critical factor is the brakes.  Coaster brakes tend to be easier for young kids to use but they become less common as the bikes get bigger.  It can be a conundrum and dangerous when kids who are tall for their age fit bigger bikes with hand brakes that they can't operate well.  After kids outgrow children's bikes they'll move into small-framed adult bikes with 26 inch, 27 inch or 700c wheels, which are sized by the length of the seat tube.

* The size doesn't have any relationship to a real measure: It is certainly not the diameter of the rim. Generally the given size is closer to the tire/tyre diameter from tread-to-tread, but it is usually greater that this distance as well. Children under 12 years going solo on a tri-cycle or bicycle have a very limited range and don't get as much pleasure from simply cycling.  If you want to have a family outing with more cycling, as you child outgrows their child seat (age 3) or trailer (age 4), there are a couple of options to consider: tandems with kid-kits on the rear seat and third wheel kid's seats.  But you will still need destinations and activities that appeal to them.  Whether by tandem or third wheel, your children will be right with you no matter how fast you ride.  On a conventional tandem both cyclists have to pedal together, so when the adult pedals the child will have to pedal, unless they take their feet off the pedals.  The third-wheel cycles are designed to be free wheeling so the child can sit back and enjoy the ride anytime they want.  For links to equipment providers go to our link section and click on "technology & innovation".