We just purchased our grand son a 110cc ATA110-B model atv for Christmas. I have slowed it down as much as I can with the screw on the handles that controls the throttle but I don't feel like it is slow enough for him to safely ride yet. Is there any other way to slow one of these down to somewhere between 5 to 10 mphs?

 

You can gear it down my changing the sprocket but your going to add more torque

 

If you slow it down too much the clutch will half engage and you'll wear out your clutch quite fast.
I recommend setting it all out, he'll learn. But really, if he gets stuck and there's not enough allowed throttle, he isn't going to be able to get out.