Myself, I don’t know. I wasn’t much interested in dolls as a kid, and I haven’t had kids. But I’ll give you an interesting little dialogue from one of my favorite movies, Ghost in the Shell 2: Innocence. Bit of background: in the world of Ghost, there are cyborgs (humans with robot bodies), robots, and humans with varying degrees of bodily augmentation.
Coroner Haraway: “The dolls that little girls mother, are not surrogates for real babies. Little girls aren’t so much imitating child rearing, as they are experiencing something deeply akin to child rearing. Raising children is the simplest way to achieve the ancient dream of artificial life. At least, that’s my hypothesis.” Togusa [who has kids]: “Children aren’t dolls!” Batou [a cyborg]: “Descartes didn’t differentiate man from machine, animate from inanimate. He lost his beloved five-year-old daughter, and then named a doll after her, Francine. He doted on her. At least that’s what they say.” Togusa: “Can we get back to reality here?” At the end of the scene Haraway’s eyes and surrounding face lift out and up, and she plugs some wires into her eye sockets.
This makes me think that there may be many yet-to-be defined complex psychological factors involved when children play with dolls. Great question.