My DD when she was 4 made a similar remark. She was in 4k preschool and we went to a theme park. We had a DW and DS in front of us and a DH and DS trying to catch up. They went right on by and my DD said "Daddy, can they do that? I thought getting in front of people in line was wrong. That's what they tought us in school." The family all turned red and asked if we wanted to move in front. We politely declined because we had been completely vindicated.
nothing more effective than a 4 yr old knowing the rules of politeness better than the adult line cutters.
What I really have a problem with is what happened to us on our last trip to WDW. We were in line for a ride, and a small child of the family that was in line behind us managed to get around us. I understand, kids get excited! However, if it was my kid, I would have called them back to our family. This family handled it a bit differently, however. The father sqeezed past us to join the kid. Then the second kid went around us. The mother kept trying to pass us as well, but couldn't find a spot to do so (she seemed a bit embarassed). The second (older) kid turned around to me and said "My mom needs to get past you." I responded "Does your mom know how to say Excuse Me?" The kid just looked at me and kept going. When we were at the ride, the mother finally said "Excuse me!" I let her pass, but I was so annoyed! Not because the kid passed us in the first place, but because I think that was their tactic to cut in line! What a great thing to teach your children!!! The only justification was that they couldn't do it to anyone else, since the mother was stuck behind us.
That has actually gotten worse since more lines became wheelchair accessible. When we first started going to WDW, many lines were not accessible and became quite narrow fairly soon after entering the line. There was very little space for anyone to cut ahead.
Now, most lines are at least 36-42 inches wide to allow people with wheelchairs and
ECVs to wait in line. We've had problems at times with people coming ahead of us to 'fill in the space' when we were trying to make sure we had enough room in front of us for DD's wheelchair to make a turn without hitting anyone ahead of us.
And there probably
are people who are using that as their 'line tactic'.
It's pretty obvious what they
are doing if the child goes to the front looking for dad and then the dad goes forward looking for the child
I've got an interesting story on a different way to cut the line - quite a few years ago I was at Universal Studios with my mom. This was a few months before I was having hip surgery so we had rented a wheelchair that day. We were going on one of the rides (King Kong I think) and were using the wheelchair entrance, which was a narrow and steep ramp - and it was also the exit for the ride, so people were walking down while my mom was trying to push me up. This young guy comes over - a foreigner, maybe German? - and asked if he could help my mom push me up the ramp. So he does and we go to wait in line and he's still there with us. The ride attendant asks us how many - my mom and I start to say 2, but the guy says 3! So he rode in the car with us - my mom and I kept looking at each other, trying not to laugh. We were thankful he didn't follow us around for the rest of the day!
Going to Disney in December with my boys who will be 4 1/2 then - I'd like to think I can "make" them go potty before we get in line, but considering how stubborn they are about it now, I'm sure we'll leaving and re-entering lines at some point.
We've had people try to do that with us - they didn't help push DD's wheelchair, but did try to say they were part of our party. At the Safari at AK, there is a point where people traveling with wheelchairs and ECVs get pulled out of the line and into a separate line to wait in an accessible boarding/unload point. It is just past the place where strollers are left. We had just passed into that part of the line when a guy behind us told the CM there that his group was with us and needed to catch up after leaving a stroller (uhh. Nice try. The youngest person in our party was a teen, who was sitting in her wheelchair and his group was only adults). When we said they were not with us; the guy pointed to a group farther ahead of us and said we were not who he meant, it was this
other group. The CM asked loudly if
anyone in the line knew these people and no one did. I don't know what happened next, but he was still standing by the CM (who was talking to someone on his radio) when we last saw.
It actually would have served them right to stay with us. They thought they would get loaded faster, but the wait in the handicapped line that day was actually 40 minutes
from that point because of the number of people waiting and the number of trams being routed to the accessible stop.
I remember going to WDW when my kids were 2 - it takes full concentration to make sure they don't end up somewhere else! Just thought it might be a useful tip if you didn't know about the backpacks. I did not know about them when my girls were smaller and spent most of those trips either strapping them into the stroller or worrying about them getting lost if they were not strapped in. It's much easier now that they are older and we don't even have to keep up with strollers! Since you didn't mention how old your DS was, it could have been a completely useless tip (no way DD5 would wear a backpack, but she is old enough that if she doesn't wait in line, she doesn't ride).
The problem most people seem to be talking about is people joining family members who have been in line for a while or sending a child to jump in front, then having the child say the mom needs to get past them (like a PP reported).
)
It's clear and obvious then that it wasn't an emergency potty break holding anyone up.
So he stood along with this couple and they all argued their point and stared each other down all the way until we got to the recording studio 
