I use Windows 8 Family Controls.
You have to create a Live account (e.g. @outlook.com, etc) and then add Children's accounts (Make an account, tie to yours). It costs $.50 to register a child account (required by COPA).
After that though, it's extremely easy to filter things based on rating or even reputation. For example, my oldest, he can browse "general" sites, whereas the younger is only allowed access to 'child' sites.
I also get a weekly activity email from M$ that shows me what sites they were on, what programs they ran, how long, etc. It even shows sites they tried to get to but were blocked. You can set login time limits, time windows, etc. They can request access to things which sends you an email, and you can approve or deny on the spot.
recommend it to parents.
Edit: Site link familysafety.live.com