I plan on renting strollers on our visit. If I visit one park in the morning and another at night - will I have to pay twice for rentals? Or, will they accept a receipt as proof that I have already paid for rental that day at the new park?
The receipt is proof that you rented a stroller for the day. Just show the receipt at the next park for a stroller. Disney only makes you pay once a day to rent a stroller.