Hi shrunkenhead
Basically I turned into an incoherent gibbering wreck, shrieking "My daughter's on the train! My daughter's on the train!"
Everybody was so helpful. First I got taken to an office and explained what had happened. Somebody phoned the guard on the train that dd was on. Then I was put on a local train.
dd was taken off at the next stop. My train went through that stop, but it was one of those very slow ones that stop at every tiny station. It seemed to take forever to get there. A guard came along not long after I got on the train - I think my lack of coat and bags, and my uptight body language made it pretty obvious who I was. He told me that my dd was being looked after and was fine.
Somebody else was there to meet me when I got off the train. I was taken to an office and there was dd, spinning around on a chair and looking ultra-relaxed.
She said later that she'd burst into tears when the train had pulled away. She was sitting opposite a lad (sounded like he was probably in his late teens) who tried to comfort her but was completely out of his depth. Luckily a nice lady from across the aisle came and sat next to her. A little while later the guard came along, told her that I was going to the next station and that she'd be taken to me. By the time we met up she'd got over the scare and decided to be very grown up and cool with me as though it was no big deal.
Although it was scary at the time we did get plenty of positives from it: when talking about new situations or getting lost we could refer to it and the fact that it turned out OK, we talked about how kind and helpful people are. Best of all, after the holidays, she could go back to school (she used to go to the primary school where I teach) and try to embarrass me by announcing "My mum left me on the train!"