I have to say that I didn't want to walk over to the DTD hotels, from DTD, in order to rent a car!!! It was just too much aggravation, and I didn't want to hike that far!!! I can't imagine anyone wanting to walk over to SSR in order to use the resort bus to the parks. Besides being wrong, it's just too far. And the DTD buses don't go to the parks, for that very reason...too many people trying to park for free and then heading to a park.
I really don't want to be rude, but how would you feel if you couldn't get a seat on the bus, at your resort, going to MK because there were people getting on from hotels outside WDW? While I understand that these hotels are 'Disney friendly' it doesn't mean they get to use all the facilities.
I would have the kids use the Grovesnor shuttle bus to the parks, or get a cab. I guess they could head to DTD, take a bus to a resort that was near the park they wanted to go to, and then head to the park from that resort. But, that could take a huge chunk of time.