The only way to prevent kids....
from seeing porn on the internet is to take away their computers, mobiles (a good idea all around) and tablets. I can't sort my email and not avoid porn (or dick pills). I have to admit that I don't see as many adult web sites in search results as I used to, but it's nowhere near perfect.
One clever or lucky kid is going to find sites with free samples and share the link with their friends. They have lots of interest, spare time and ADHD when it comes to things they know are naughty.
"Stack the Fridge and Stoke the bong, we're stayin' in tonight." or would it be "My Dick's on the Dole (livin' on hand outs again)"?