That is really interesting behaviour. And totally not ok or normal or anywhere close to polite!

I reckon that the sight of the lollies made people regress back to childhood so they acted like it!

Also, people seem hardwired to want to keep their place in line, any line, and make sure they get their "share". In groups this can be really strong. No one sat down so no one sat down IYKWIM? They were all sharing the responsibility to be polite and appropriate. Because there was a lot of them, that responsibility got diffused or watered down. If there had only been two or three people waiting to get lollies, they would have sat down a lot sooner because a greater share of the responsibility would have fallen on each of their shoulders. One way around that type of situation would be to name each of the people in turn - it reminds them that they all have an individual responsibility to behave appropriately. People think they're anonymous once they're in a large group.