This looks fun and the reviews are good too...
The Halfords Mini Racer Electric Bike is great for your child to get around on and speeds up to 1.5 mph. It is suitable for ages 3+.
Features & Benefits of the Electric Mini Racer Bike
Motor 1 x 6v battery
Maximum speed: 1.5 mph
Front and rear light with sound effects for added enjoyment
Rechargeable battery and charger included for your convenience
Suitable for ages 3+ (up to 30kg in weight)