Its up to parents to be pc, mobile, & x box savvy
and there it is....don't buy your kids internet able devices if you don't know how to monitor what they're doing or at least think about sensible ideas that will reduce the risks.
Keep that stuff out of the bedroom so they are in the family space when using them and take them away in the evening. Devices make life much more difficult to monitor compared to computers, I had a virtual network so I could monitor what was going on remotely from my pc, you can have logging of chat programs which even send you the chat history by email