It seems your thoughts on this largely depend on your own view of children and sexuality, which I can tell is different from my own. To me, we're all sexual beings from the womb, and again I feel the need to separate sexual and sex. It sounds to me as though you're equating slash with sexual with sex. While I equate slash with sexual, I don't equate it with sex. While sex can be contained in slash, sex is not the entirety of slash for me. Therefore, it's entirely possible in my eyes to have two characters of that age with a slashy vibe of sexual subtext. I'd probably have issues writing it, though, so I can see why it's causing you problems.