I haven't read all the responses but we are going in September with our 3 and 6yo and we are absolutely renting a double stroller. The 6yo rides when she's tired but also it's a good place to sit when we watch a parade or grab a snack and can double as an umbrella if it rains (which it most likely will in September). I would rent a double. Most deliver to you and pick up and come with a rain cover. My husband thought I was crazy for our last trip bit he said it's the best money we spent on the trip. It's is a TON of walking. I hit 30,000- 40,000 steps a day. You will not be the only ones with older kids in a stroller. Our daughter gets the same pains...just growing pains after particularly active days. She didn't ride that much this last trip but it was nice to give her the option. And she's an active kid normally. We play sports, go on walks and bike rides. And sometimes it's just easier to plop 2 kids in the stroller if it gets a little crowded. I'm actually surprised at the people thinking it's strange. I just think it's a good option to have just in case...plus it's great storage!!! That being said...it's likely he will want to walk since there is so much to see.