How to block accessing to age restricted website using C++ app?

I have created an app that blocks websites that contains age-restricted words. I'm using Proxy tunnel to detect site content and change it if some words was detected. But It's not good idea for me. Because some users use it's own proxy server on his computer. And if he changed the proxy server settings the program doesn't filters websites. I researched web about "How to block accessing to pornographic websites". But all results:

• uses hosts method which I can't filter website content to detect it was safe or not
• tells using windows kernel based hooks but doesn't tells how to use
• using proxy, but user may need to change proxy settings then app can't filter

How can I use hooks to block accessing to website by filtering its content?

And also I looked different parental control apps which doesn't uses proxy or hosts file to detect suspicious websites.