9503 is a toy, and the scooter you mentioned should belong to the wheeled toy mentioned in the tariff notes. These toys are usually pushed by pedals, manual rockers or other simple devices, and the power is transmitted to the wheels through chains or connecting rods.

9506 includes supplies and equipment for general sports, gymnastics, competitive sports and other sports (including table tennis) or outdoor sports not listed in other items in this chapter. It seems that it can be classified as 9506, but this is a commodity that should be classified as 9503, so it cannot be classified as 9506.

(only on behalf of personal views)