For lines, and even some walking around, you need to get a soft baby carrier! He's probably getting a bit up there for a side-carry sling, especially if you haven't gotten strong as he went along, holding him like that.
But a mei tai or an Ergo or Beco, those are *perfect* for littles in line. During our trip when DS was around 17 months old, he loved the mei tai. He could see at our height, he was safe and secure, and I could easily take him out of it. He loved not just seeing our bottoms from the stroller, but to be able to see the decorations in the lines.
Places to crawl. The chip and dale treehouse in ToonTown. NO one goes in there. Goofy's House. Watch out for him though, there are bigger kids who like to run!
There are also places for semi-safe crawling in the Redwood trail area in DCA, but again, you have to watch out for the crawler with all the bigger kids around. Also watch out and be prepared with even more extra clothes than usual, b/c there's water on crawling level too.