Wheelchairs can be brought to the point of boarding and left there. A transfer is required since there is no wheelchair accessible boat.
It’s not an easy transfer - there person has to step/be lifted over the side of the boat and then down to the seat.
A baby could be held on the lap, but a larger child would need to be sitting on the seat.
There boats have bench seats and should be able to sit 3 - one on each side of the person who needs support.
The wheelchair can be placed as close as you need to the the ride vehicle. After riding, the wheelchair will be near the unload area, which is just down from where you loaded.