It depends on so many things. If there is enough room for them and they're not standing in an unsafe place, if the blades are down on the mower, if the scooter isn't going fast, how old the driver is, if the parents know beforehand exactly what is planned, and more.
If my girl was going to a friends house and they were going to ride 4 wheelers I'd say no. Not unless I was there or had been there to see what sort of supervision the kids would have. If the kids were going to ride them and not wear helmets then I would never let her do that. If I knew the parents made their kids wear helmets and they kept the things where they were only in the lowest gear and couldn't go fast then I might let her ride without me being there.
When I was a nanny I would bring the kids out to the farm we would take them on the tractor all the time. We had a wagon sort of thing we could pull behind it too. We NEVER had the mower blades down when they were anywhere near. But they did enjoy riding all over the property in the wagon.
Golf carts go pretty slow don't they? I would think if a parent was driving and the kids were sitting down then that would be safe too.
It really depends on what the parents expect and what is planned as the activity.
No to any sort of scooter that is 2 or 3 wheels.
Our girl has been driving the pickup and van around the farm since she was about 10. She isn't allowed to drive it by herself but if we have our hands full or really dirty then we let her drive us where we need to go, like the other house or the barn. She is pretty good. When it comes time for her to take her driving test she'll pass just fine.