My nine year old loves rides and has no problem with single rider. But not all of my kids would have been ok with that at 9.
If you have more than one adult, put the 9 year old in between. Have a meeting point for after the ride- photo screens or whatever. Somewhere they can communicate to a CM incase they need help.
If you have more than one adult, put the 9 year old in between. Have a meeting point for after the ride- photo screens or whatever. Somewhere they can communicate to a CM incase they need help.