Depending on how many websites your children actualy visit.. you could use a workaround..
It's very messy, and isn't ion the slightest bit helpfull unless your kids only visit like 5 websites..
But.. if you go to tools > options > connection settings
Enter a random IP for a proxy, so that no websites will work.
Then under 'no proxy for' enter the websites which you want to allow.
As I say, very bad and messy
