My daughter first expressed interested in dolls at around 15 months. We didn't have any at our house, but my Mother had several that really intrigued my toddler.
Now at 25 months she has two dolls at our house, an assortment at my Mothers and two at her Dada and Dadi's house. But, she has numerous "babies" that she lovingly tends to at home. These include: a praying mantis, a rat, a field mouse, a pink hippo, a cat, a pink bear and a monkey (all presents from our generous family and friends).
She adores putting her "babies" to bed, carrying them around in a toy infant seat carrier (that I got for $6 at a thrift store), giving them baths in a "tub" and pushing them around in a toy stroller.
It was an easy decision on what to give her as a present to celebrate her new role as a Big Sister (when her Baby Sisssher finally arrives). I found a "mini-Ergo Baby Carrier" that matches mine (except hers has some cool stars on it). We've talked a lot about what her Baby Sissy won't be able to do (like walk and talk and chew food). And, she knows that Mommy will have to carry the baby everywhere.
I can't wait to see my Big Girl wearing her very own Ergo. It will be interesting to see which of her "babies" gets carried the most.