For the first year, well, really year and a half of Back Seat Boy's life, Back Seat Girl really didn't seem to take much interest in him. She wasn't jealous of him, she didn't dislike him, in fact she did profess to love him. There just wasn't that much interaction going on. I remember at one of BSB's check ups the Dr was asking me how BSG was doing with a little brother. When I told him it bordered on indifference (BSB was probably only 2 months old at this point), the Dr told me that was pretty normal. To a 2 year old, a baby is like a broken toy. It doesn't do much but eat, sleep, poop and cry. And it doesn't do those things when you tell it to, it just does them. BSG likes things that do what she tells them to.
After a while BSB began to crawl and stand up and play with things, and that increased their interaction a little. I remember one night I was cleaning up after supper and they "chased" each other around the house, BSG walking, BSB crawling. It was just a glimpse of what I get to enjoy now.
I don't know when it happened, but the two of them see to be forging a beautiful relationship. They play together, they talk to each other, they hug each other good night. BSG has even said things like "I love hugging [BSB]". Yesterday BSB kept going up to BSG just for the sake of getting a hug. If BSB sounds like he's in distress anywhere in the house BSG is constantly asking me to go and help him, and gets mad if I take too long. She is always trying to teach him new words and or how to play hide and seek correctly. He is also very often unwittingly the dad to her stuffed animals. She sends him off to work and receives him back "home" (her room). I really don't think he knows what's going on half the time, but he loves it because he loves playing with his big sister.
They definitely have their squabbles (the one toy the other has is THE BEST toy every created in the history of the world and I MUST HAVE IT), but I know they love each other. When they grow up they'll be able to talk about how crazy mom and dad were (are) and can you believe we lived in that tiny house with one bathroom or how much fun they had on our camping trips. I love watching them make memories together that they'll be able to talk about with each other long after Driver and I are gone. I love watching them form this bond that is so unique to being brother and sister.
I really hope they don't have too much to discuss in the 'Mom and Dad are nuts' area, though.