I think the usage of "child" and "I was only 10" are meant to be metaphors. I think Stevie's writing about the love affair and subsequent breakup that finally made her grow up. I think we've all had that one really intense love that forever changed us, made us view the world through different lenses, and most notably...
matured us. After the loss of your first true love, there's also an enormous loss of innocence... and I think that's what this song is about.
