I know that this opinion is unpopular, but, all I can say is hoorah! Six and Eight year olds riding around on their butts instead of getting exercise, in my mind, is almost criminal. We have a new generation of over-weight, lazy kids that expect everything to be done for them. The one's with the legitimate gripe are the one's with little tiny, young children. The first time I visited my kids were that age (6 & 8) and frankly it never even crossed our minds that a stroller would be necessary. And it wasn't. Taking a longer break is the answer, I'm sure.
If the cost of the motorized carts goes up there are places outside of Disney that rent them for very reasonable rates. It might cut down on the abuse of those as well.
I'm not sure it's true anyway unless they held a high pressure meeting and decided that the problems they were causing weren't worth the revenue. Ankle injuries alone could be mind boggling. If they don't rent them, they won't be liable.