This is a great idea. Here's mine:
-One day, when I was pregnant with my second, I was sitting at the Kitchen table with my 3yr old daughter eating lunch. We were talking about something or the other. We got onto the subject of eating and teeth. I told her that her sister won't have teeth for awhile so won't be able to eat like us right away. Then I said something about when she was a baby. She looked me dead in the eye and said "I was a baby once?"
I about fell out of chair laughing so hard. It was so cute the way she said it, too. You could her the shock in her voice.
-My 3yr old has a step stool in front of the bathroom sink. One day she was being goofy as usual and fell off of it. (She didnt' hurt herself, though). Well, my then two month old daughter was sitting just outside of the bathroom in her bouncer seat. Would you believe, she actually started laughing at her sister. LOL. I started laughing, too, and told my oldest "Your sister is laughing at you." Then she started laughing about it as well.
I guess it starts early for siblings to get a kick out of the other getting "hurt."
-T.