Here is a 4-wheeler designed with kids in mind. The Offroad Mall REX 110cc ATV is made for kids 10 years old and above. It features off-road air-filled rubber knobby tires, steel rim, headlight, and taillight for night driving. It has max speed of 34mph and can handle up to 132.3lbs of load.
The Mall REX Kids ATV has front and rear suspension with spring shock to give a smooth ride. It has an air cooled engine to prevent overheating. It measures 48.8″×32.7″×28″. You can find out more about it here.