Choosing a Bike for a Child
From bikes with training wheels to teen-sized versions of adult bikes, there are many options available for kids. The most important consideration when buying your child a bike is size. When shopping, keep in mind that children's bikes are measured by their wheel size, not frame size. The most common wheel sizes are 16", 20" and 24". The right size is one where the child can comfortably get on the bike and stand with his or her feet on the ground.
It is not recommended that you buy a bike that is too large for a child and then have them "grow into it." Doing so can set the child back in terms of riding skills and confidence. A properly sized bike will be easier for kids to handle, less dangerous and a lot more fun. And don't forget the helmet!
For beginning riders, see the REI Expert Advice article and video, Teaching a Child How to Ride a Bike.