You know your own child best. We went a few years ago with an 11yo, just-turned-7yo, 5 yr old, and 2 yr old. We brought a stroller for the 2yo, and intended to rent a WDW one if necessary, for the 5 + 7yo. We did 7 park days in a row and never rented a stroller, they just didn't need it.
Last year, we went and the kids were just-turned 13, just-turned 8, 6, and turning-4. We brought the stroller thinking the 4yo would mostly ride, and the 6yo could ride periodically if he needed a break. Well, for 8 parkdays in a row, we pushed a stroller with Pal Mickey in it. Not a single child's bottom touched that stroller seat.
Next trip, we will just forget the stroller. We will budget $ to rent one, on the off chance we need one. (It will be WONDERFUL to not lug a stroller on and off the buses!)
Beth