Kids' bikes are typically sized by the size of the wheels. The smallest pedal bicycles usually begin with only 12-inch tires, while larger bikes go up all the way to 24-inch tires. Some even make smaller kids bikes when your kiddo isn't ready for a full grown bike. Still, no matter the size, all kids bike sizes should have pedals that are made for children of that age. The size of your kid's bike depends on your child's height and weight. You want to be sure that the seat and handlebars can handle your kids' weight before you buy them. Some bikes are made bigger so that they can accommodate growing riders. Before you decide on a bike, take these factors into consideration.