The issue you have is occupancy.
The trundle rooms at POR are available to parties of five. So are most deluxes. The FW cabins and the all-star suites I believe have an occupancy of six. More than that and you're looking at 2-br suites at DVC resorts. Kids over the age of three count in the occupancy count, so the POR is kind of your only option unless you want to pay more.
It's not that you couldn't pack an air mattress and pile the kids on the floor - it's that Disney will not allow you to book a room with an occupancy level lower than your party size.
None of the resorts offer cots, although last september at POR when my adult friend took the trundle (she's short) they did bring us all kinds of foam padding and extra blankets so she'd be comfortable - I suppose you could make a pallet for one of the kids with that? You can also bring air mattresses from home if that seems like a better idea, although with the floor space available in those POR trundle rooms when the trundle is pulled out, you may have a real problem fitting it anyplace other than a twin-size in the walkway between beds and tv (which is the direct route to the bathroom).
