Kids bikes are sized by the wheel size, not frame height, and are designed to accommodate a large range of sizes. As a rough guide 12" bikes are for 2-5 years, 16" are for 4-8 years and 20" are for 7-10 years but check the inside leg measurement and saddle height range to be sure. Pedal-free bikes are an excellent way for small children to learn balance and steering skills before progressing to a normal bike, usually without ever needing stabilisers, and are perfect if you have some gentle flat and downhill stretches to help them enjoy coasting along. Young children often find hand brakes difficult to use, and are better at stopping with their feet, so set the saddle to a comfortable height to allow them to put both feet down.