The CX kiosks in SYD (for Y class) mess with the order of the queue. It's difficult to explain in words but it has to do with people who arrive first going to the first kiosk they see, then joining the back of the queue behind people who haven't used the kiosks yet. Meanwhile other people skip the queue and go to the kiosks that are further ahead, then butt into the queue at the point where the kiosks are.

When the queue is short, some people push their trolleys to the front and then go back to the kiosks, blocking the path through the tensa barriers.

The kiosks don't allow you to check a bag for a child either, so if you want to do that you have to go to the desk anyway. In HKG that involves arguing with the untrained staff who say that children can't check bags at all (despite the ticket clearly saying allowance 1PC)