I've seen enough hentai to know where this is going :V
But, anyway, I managed to fix the problem. They aren't considered children by the game anymore, but by removing the child flag from them, using another follower mod and by adding them to the follower npc group they can still follow me, and actually be useful in combat (if you change their confidence and assistance, that is). I got an follower overhaul, so I can put both of them and even more people in the party.
I got a female kitty, too. I just need to find all the materials to craft her things, no skimpy armors for her >_> Their morality is set to 0, so they'll do pretty much anything.