The first day I was home alone with my new baby son I forgot his name, the one I had chosen! I knew it began with A, so I went through them all, "Hello baby Andrew, Arthur, Allan ..." none sounded right and I realised one of the congratulation cards had his name on it, so had to go and read them until I found it!
A couple of years ago, I also introduced him to my art tutor "This is my brother and his wife - no it's my son!"
When I walked home from the school where I taught, I left my daughter sitting waiting patiently for me. My mum was staying that night and I thought she had picked her up. We spent 5 minutes looking for her, both thinking that she was playing Hide and Seek and playing along with it, until I realised my mum didn't actually know where she was. Phone call to school and mad dash to collect her!