My son had just turned 5 when we went in 2013. I couldn't figure out what I wanted to do, he would complain here at home when we would be somewhere "Carry me". I kept going back and forth, to rent or not. Finally, I just decided we are going to be there for 10 days, we would give it a day or two and see how it went. I could always have a rental delivered to the hotel. He didn't complain once and the only time my husband carried him was the night we did the Electric Parade and it was very crowded and it was just easier.
Now, we toured at our kids' pace. We did rope drop every morning, did mostly late character breakfasts, and toured til 1-2 pm and went back to the hotel to relax. We did different evening things, but only two later nights (after 9). I know my kids. My youngest needed to be in bed by 9:30 or the next day would not be pretty.
So, you know your kids. If you are going to be at the parks open to close, a stroller may be needed. And if you want to wait and see you can always change your plan when you get there. I'm glad I waited because it was an expense we didn't need.