We had similar situation where we had missed our train with allocated seats from Scotland to Bristol. It was an arranged group camping trip and the coach driver was late picking us up from camp. So we decided as a group and told all the kids who were ages ranging from 6-14 that when the next train got in which was ours that they were to just to get on it and we would find them. This train was an absolutely packed commuter train. So us and another family chanced getting on and luckily so did the kids but we lost each other as we got on and it took a frantic 5 mins of our hearts thumping like mad before we all got together. We had to keep swapping seats all the way but got home tea time ish. Unfortunately, 2 other families didn't get on and got back to Bristol midnight ish. That was about 15 years ago and my daughter still remembers it vividly.