I will never forget right after my son was born (literally just a couple minutes). Normally I've got a camera in my hand when there's some sort of family event happening but not this time. My daughter, who was then 3 years old, was at the hospital waiting for her little brother to be born and her grandparents were keeping an eye on her. When they came in, she was all smiles and said "I'm a big sister now." I'm so glad I did not have the camera going then because the memory of it has stuck with me so well and I would've missed it if the camera had been going. I can hear her voice just as clear as day these 12 years later.
Fast forward 12 years from then, and they fight quite a bit, but don't let anybody from outside the family mess with either one of them! They are the first ones to come to the each other's aid when someone outside picks on the other one.