It doesn't matter how many fixes you try to fix in current android, it will always be insecure. Google Play won't work for 4.4 so the kids won't install any app. Blocking sideloading will make the kids unable to sideload. All they ever have is and android phone with the heaviest browser restriction, any website not on your list becomes block. Super simple, the fear of insecure is only from people who can't control the phone 100%.