blank Parental Controls log display
I ran into this same problem with my son, I googled and found a post where someone suggested to check 

MacintoshHD/Library/Application Support/Apple/ParentalControls/Users


But when I did I found that "Users" was locked.  I tried to chmod the settings to 777 and was blocked, so I sudo changed the settings with:

$ sudo chmod 777 Users/


For the non-native terminal user, first open the terminal by searching for it with Command SpaceBar.  Type terminal and open it.  Then type (hitting enter between each line):

cd "/Library/Application Support/Apple/ParentalControls"
sudo chmod 777 Users/


Then access the parental controls through Settings.  You should see the webpages now when you click Parental Controls, then the child's account, then Logs (lower right corner), then Web.