The child that Gin found was Matsumoto. Nobody else. She was referring to herself in the third-person, as a child, not as the adult having the flashback.
And I thought you had to have died in the world of the living to wind up in Soul Society, and ended up by yourself in the outskirts with some makeshift family you're not related to at all, wandering alone, etc.,... or did I miss something when watching the SS arc?