I posted about this a few months ago, but I wanted to mention it again. If you have had kids that have an iOS device, I highly recommend you subscribe to Curbi. I interviewed one of the developers on the most recent episode of Out of School and I highly recommend you listen to learn more about it. It's only $50 per year for 5 devices. It does a lot of interesting things to allow you to have control over when you kids can access certain kinds of content. It also blocks adult content by default. It works over LTE and WiFi and does not require a special browser. It works at the device level rather than inside of a browser.