The tires are what makes the most difference in the ride. If the tires are larger than average and made of rubber, then they will do better on ground that is rough like gravel. If the wheels are a lot thinner and harder rubber, then the scooter will do better on well-paved roads, like in the neighborhood.
Each scooter has a specific type of terrain it is built for, which is why it is important to know the elements in which you will be riding your scooter as well as how far you want to go. In order to have a smooth ride, you should also consider how long you need the battery to last.
If you plan for your kid to ride his scooter alongside you for longer distances on trips to work or school, then, of course, the scooter will need to have a high-quality battery that lasts a very long time while in use.