It isn't great - some countries in Europe just don't do queuing. Brits are known for our polite queuing!
I agree with the above about it getting better at DLRP, especially with character meets, lines are formed and the CMs try hard now to keep it in check. I also found at character meals that handlers, and more often than not, characters themselves would ignore a child butting in, or point them back to their table etc.
I've only once lost it at DLRP over queue jumpers. It was waiting to go into 'Meet Mickey Mouse' at the Town Square Theatre. There huge queue snaking around the ropes in the building where they show the little cartoons while you wait. The queue was over 40 minutes - we only did it this once as we didn't know what to expect as it was new, wouldn't bother again as we always saw Mickey at Inventions or in the DLH (before they took characters out of hotels). This Grandpa, Grandma and Daughter and Son In Law (no kids), came in and decided to just jump under the ropes and cut between people. I was furious to see them not just jump one line but 4 - no joke! What made it worse was that people were actually moving to let these people do it rather than say no! I had to say something and a British family next to me did the same but they just pretended they couldn't hear our calls. We finally got to the CM at the front of the queue and told her what had happened - of course by this point the said family had been and gone and we'd queued another 30 mins with two small children.... The CM didn't seem bothered at all!
So yes, it happens. But I do believe it is improving. And for what it's worth - I've had it happen twice to us in WDW last summer too - young groups of Americans - once pure cutting in, second time 1 person in queue, 6 turn up to jump in after 15 mins!
As others have said, I try not to let it bother me where possible....