I know I was being unreasonable but I’m not sure how else I should have dealt with this.
I took my three year old and nearly 1 year old - not yet walking - to a museum. It wasn’t pram friendly so had to carry her round and she’s heavy. Three year old went round and enjoyed it and then wanted to go back in. It was a one way system so was trying to explain to him he couldn’t get in through the door he was trying. He ended up having a tantrum. Eventually he shot off and ran in through the right door, I tried to follow but a crowd of people got in my way and when I eventually caught up with him I was saying his name over and over and he was just blanking me. In the end I shouted STOP IGNORING ME and dragged him out 
I am not sure what else I should have done.