I have 3 kids, ages 6 to 13, and this has been important in my home.
The first and most important thing is communication. You need to talk with your children about what is appropriate and what is not appropriate as well as what the household rules are for internet use.
In my home, I also have a rule that all devices are subject to "spot-checks"
at any time. I rarely do this, but the knowledge that I can and do check
on things serves as a deterrent to inappropriate internet use;
especially on social networking sites. For device specific controls, I recommend K9 Web Protection in conjunction with setting restriction on each device. Desktop computers need to be in public areas where anyone can see the screen; mobile devices are more difficult.
As there are multiple devices and platforms, controls on one device are often insufficient. I use router based tools to cover my entire home network. That does not mean you should not make use of device specific parental controls, but those can be inadequate.
For filtering, I use openDNS. This works at the level of the router to provide filtering across the entire network and is highly customizable. You can select from over 50 categories to block anything from pornography, drugs, weapons, and hate/discrimination, to more mundane topics such as blogs, photo sharing, etc. You can also fine tune this by adding sites to always block or never block if certain sites need to be blocked or allowed despite the filters.
To manage time restrictions, I use a set of excellent parental controls on my router. I have an ASUS RT-AC66U router, but there are other options for good parental controls on a router. With my router, I can manage time restrictions that are device specific, so all devices my kids use have no internet connectivity during "bedtime hours" as well as an hour after school set aside for reading and non-internet based homework. Device specific settings enables me to have different time-windows for the 13 year old and the 6 year old.
No single tool is bullet-proof, nor should you insulate children in ignorance. Children lack the experience and wisdom of adults and should therefore be educated about the potential dangers of the internet and also protected from inadvertently stumbling upon inappropriate material.
My 5th grader recently copped to looking at "naked pictures" on the web and was also told by a friend how to delete web browsing history. I don't want to be a total prude, keep my kids under constant surveillance, or force my kids away to phones or friends homes to use the internet. My kids ages range from 5 to 14, which makes this issue even more difficult. I have a Windows 8.1 desktop and Windows 7 laptop and a few Android tablets. Maybe just some piece of software that restores browsing history would be enough. Any advice on sensible (and preferably easy) ways to monitor and/or censor kids internet usage? Anyone have a good tried and true recipe they have used?