Here is the solution for your kids. You can download and install the KIDO'Z Browser in your Computer.
Features of KIDO'Z Browser :
Safe & free internet browsing for kids.
Easy to use. Kids don't need to know how to read or write.
Direct access to the best sites, videos and games for kids on the net.
When you first download and install the browser. And run it, A little window should pop up asking your your child's name, and the parent's name and email. just fill in those detail's and your ready to go.
It needs Adobe AIR to run this browser.