You know your kid best!
Most people favour strollers for kids and I was so worried to eschew this advice our first trip. However just in case anyone has a kiddo like mine I'd like to share. We've now been with DS 3 times, and we've never brought a stroller. DS is a high energy kid, he never stops moving and has a difficult time sleeping at night- except at Disney! We don't go back to the room for naps and we go from rope drop until fireworks. Also, because he is our only, we are able to carry him for a few minutes here and there if he gets a bit tired. And another point is that he has always been very good at listening and staying with us, he knows our phone numbers, would be able to get help if he got lost etc. On our first trip when he was 3 I did bring a woven wrap, but he walked a ton even at that age, it was mostly just so he would crash at the parks and DH and I could enjoy fireworks. Our last trip he was 4.5. I absolutely love not having to push a stroller!
If you do decide to go sans stroller, definitely make sure you "train" them a few weeks before. I make my kiddo walk lots to train before vacations by walking around our neighbourhood and the like! If your kiddo is not used to walking distances, or you use the stroller at home, I definitely wouldn't go cold turkey for Disney. And check them for blisters! Even adults get them with that much walking, and a young kiddo may not know why their feet hurt so much.