You didn't say anything about where you are staying or your transportation. Any of the companies that SueM listed will deliver the
ECV (which is the abbreviation for Electric Convenience Vehicle, often called a
scooter) to your hotel.
I have always used Walker. Randy's is less expensive, but they require you be present when the ECV is delivered and sign a waiver of laibility. I think they also require you be present when they pick it up. OTOH, Walker's (and I think the others) will drop it off at your hotel Bell Services, whether off- or on-property, so it is there prior to your arrival and will pick it up after you depart. Daily rates are comparable to Disney's charges, but you save on a week or longer.
If you are driving, as long as you have a large intermediate or larger car you (or your husband) can quickly break the ECV down into five parts, the heaviest 39 pounds, and put it in the trunk of the car. With practice, it only takes about a minute or two to break it down and put it in the trunk, and a couple of minutes to set it back up.
If you are stating on Property, the monorails, almost all buses, and all but the smallest boats can handle an ECV. If staying off-property and will not have a car check with your hotel about accessible transportation.
Most of the lines you will be able to just about all the way through while seated. Some attractions you might have to transfer or walk, but that should not be a problem for you; the key thing is using an ECV you will not have excessive standing.
As SueM also said, your husband can handle the stroller and 5yo. You do
not want to use a wheelchair.