My dear sweet baby girl was only 2½ years old when we decided to completely turn her world upside down and make her a big sister. It was a role I wasn't sure she'd want to handle, but she embraced her new title and her new little brother with open arms.
As the only child for over two years, I wasn't sure how she was going to handle sharing all of the attention she had gotten so used to receiving. So I, along with my husband, decided we wanted to slowly transition her into the idea of having a sibling. Before we even got pregnant, we used to ask her if she'd want a new baby brother or sister, and she was always very excited at the idea. Then when our friends welcomed their third child, we made sure to arrange several play dates, so she could see what it was like to have a baby around.
The final act, and I waited till I was safely out of my first trimester, was to take her to the store and let her pick out a baby doll. We must have spent 30 minutes in that aisle while she carefully examined several dolls. We praised her for how grown up she was and talked about how she'd have to be gentle with her new special doll. And when we got home, we told her she was getting a new baby doll, because mommy and daddy were having a new baby. Much to our relief, she was ecstatic!
I was so incredibly proud of my little girl at this time. She loved helping me prepare for the baby, and she told everyone that she was going to be 'the big sister'. There was only one small hiccup with her accepting the baby: She really wanted a sister, because all of her friends had baby sisters. So to help her, we purchased a couple books about having a baby brother. And when we'd shop, I'd let her pick things specifically for a boy like clothes, blankets, and toys. Though it took awhile, she eventually got over it and couldn't wait to meet her little brother.