Folks, this is a vacation--not a top secret covert mission.
Take the kids to the bathroom.
When my kids were little we always did a pit stop whether they needed it or not. The rules here were simple: use the bathroom and wash your hands, or we weren't getting in line. No bathroom use, no line.
In the unlikely chance one of the kids needed a restroom break while we were in line, we left the line. Actually had this happened once, at the very front of Buzz Lightyear. DH had been in line for about 45 minutes with both kids. DS (about 7) wanted to do the ride badly, but DD (about 5) decided she had to go to the bathroom and could not ride. DH took both kids out of line, because DS was too little to ride on his own. DS, now almost 16, still remembers it.
After that incident no one ever got in line without a restroom break.