One of the most common mistakes people make when buying kids’ bikes is getting a bicycle that’s too large, so the child can “grow into” it. This might work for sweaters, but not for bikes! Bikes that are too large are difficult to control. If a child can’t control a bike properly, they won’t be confident riding the bike.
The first step in picking a bike is getting the right size. Bikes for children are sized by their wheels: 12”, 16”, 20” and 24”. The rider should be able to get on and off the bike flat footed. The child should not be riding scrunched up with their knees hitting the handlebars and they should not be stretched out and unable to turn the handlebars easily.
The most important mechanical parts of a bike, overall, are the brakes. Kids’ bikes usually have either coaster brakes (brakes on the back wheel that are engaged by pedaling backwards), or handbrakes (brakes engaged by a grip on the handlebars that pinches brake pads against the rim of the wheel) or both. Because of their small hand size and limited hand strength, the smallest kids’ bikes have coaster brakes. Before they move up to a multi-speed bike with a derailleur it is good for them to get some experience on a bike with both types of brakes so they get used to hand brakes, because bikes with a derailleur can only have hand brakes.
Bike shopping tips: If at all possible, take your child with you when you shop, so he/she can try out the bike.