Mountain bikes, with their tough construction and multiple gearing, are probably the best bet for older kids who will spend hours at a time in the saddle. The Mongoose Stormer is a 24-inch bike that makes a good transition for ages 10 to 12. This will allow the child to participate in longer rides accompanied by adult cyclists. Choosing the right size Getting the right size of bicycle is critical for safety and comfort. The wrong size may cause your child to lose control and be injured.
Oversized bicycles are especially dangerous.
Straddling the center bar, your child should be able to keep both feet on the ground with at least one inch of clearance between the crotch and the bar. When buying a bike with hand brakes, make sure that the child can comfortably grasp the brakes and apply sufficient pressure to apply the brake. Make sure that the child has adequate steering room. The child's knees and body should not prevent the front wheel from turning at least 45 degrees to either side. The child should be able firmly grip the handlebar throughout the turn.