Reading the comments on this question, I suppose it's more a question of how you use your imagination. I, too, observed that other children seemed to play either by acting out social roles (playing "house") or by picking up ideas from other children, if that makes sense.
I played "make-believe" all the time - by which I mean I populated several worlds with peoples, cultures, scientific laws, history, and so on. My notebooks have pages and pages of language notes, alphabets, "cultural" drawings and invented field notes. Every sketchbook had its own small doodle government, that regulated the doodles from taking over the nice pictures. I made civilizations out of nut shells and dirt, and Lego blocks, ignoring "set" toys, and played at being an archaeologist by stealing broken dishes, burying them in the yard, and digging them up again. I had a little sister, which was entertaining, and we played Barbies, but never "house" Barbies. It was "Dr. Barbie Gets Lost In The Jungle And Eaten By Cannibals." And the Barbies had a specific culture, political system, and they all had fixed names, and we moved the game along by saing "Make her say..." to each other, so that it would go where we wanted.
Children's games from outside my family made no sense to me, unless I could create and dictate them. Still, the way my friends in college create seems strange. My friend, R. writes fantasy, and she says "characters just walk into my head" and she spends more time fussing over their identities than anything else. Whereas I know my characters' histories and worlds in great detail, but neither know nor care how, for example, they feel about their mothers (and if I do know/care, I'd be able to sum it up in a sentence or two, instead of talking about it for three hours).
Does any of that make any sense?
I'm totally avoiding editing/writing right now, so...