I've had a pig of a day traveling with the family including DD (6). She totally kicked off on the pane when we were coming it to land. Hitting her brother, kicking the seat in front, trying to undo her seatbelt. DH had to restrain her which resulted in screaming. You can imagine - it was awful.
We got off the plane and when we got to paspprt control there was an incredibly long, snaking queue. I just knew we were going to have a repeat of the plane. I found a woman behind a desk, told her my daughter had SN, had just kicked off on the plane and that I didn't think she could cope with the line. She simply said not a problem and took us to the front and we went to the next available person. Honestly it saved my sanity when we all had very little left. And it was so great that she just accepted what I said with no questions and sorted us out.