I would actually not use a stroller. I’ve found it’s more annoying to track down stroller parking all day long than people think. If your 6 year old doesn’t have any physical issues, I would suggest doing a walking program to get ready for the trip instead. My 7 year old “trained” for Disney by doing 20,000 steps per day in the months leading up to our trip. It was cute to see him running around the house to get his steps in. And he had no issues keeping pace during our 7 days in the parks in August. We do a table service meal at least once a day though, which is at least a 1 hour break.