StayFocusd is an amazing Google Chrome extension which blocks websites automatically. Did not get it? Well, you can make this extension to block any website once user exceeds any particular time limit.
Say that your kids spend a lot of time on websites like Facebook and some online gaming websites. Then, you can use this Google Chrome extension which would automatically block any mentioned web site after mentioned time.
If you do not want your kid to spend not more than 60 min for playing online games, StayFocusd will will let him play more than that.
So, if you want to block websites on Google Chrome the way you want, then this extension, StayFocusd is one of the best way to do that.