My daughter has been bringing dolls and teddies for me to nurse for a long time, since maybe a year old. It was later that she started having teddies and playmobil people nurse eachother. She only recently (she's now 27 months) started nursing them herself. Always treats that as a big joke, whereas she sees it as normal behaviour when teddy asks to nurse. I think it's a big imaginative leap for her to get the idea of "nannies" existing anywhere other than on my body.