Children can use it from as young as 2 or 3 for the Mini model. The Classic model is usually for kids from 4 years of age or taller than 3 ft 3". We recommend the Drifter model for kids older than 6 and the Pro for ages over 9-10. The seat of the Mini is good up to 35-45 lbs so a tall 3 year-old could be more comfortable on a Classic than a Mini. Then the Pro models are probably better once the child is over 110-120 lbs because it has a wider seat.