I will be in a similar boat, as we'll have a 2.5 year old and will be reinforcing potty training still (most likely). My plan was to get in line with my mom, aunt, and husband, then have two of us wait in line while two take her to the restroom, and make sure to tell the people behind us what we're doing so they will know we're not just jumping back in line in front of them, etc. I would think most people are very forgiving of potty breaks in line, especially with little ones at Disney, if they know that's what's going on. Just be friendly and courteous, and most people are the same way back!