We do not service pornography, unless you're explicitly searching for it. There are obviously some terms where there is some overlap, for example, like “cougar”. We make sure to demote the pornographic sites on that term so that you don't stumble upon it without having intended to do so.
With child sexual abuse imagery online, we've partnered with a number of non-profits to develop a pretty robust database that allows us to identify those images or those pieces of content with something called “hashes”. That's a partnership with Facebook, Microsoft, and Nik Mic in the States. We don't service that content at all, globally.
With underage people accessing pornography, we do have settings in our products that you can use so that it will never surface. There's something called SafeSearch; no pornography will surface when it is turned on. When that is turned on, it automatically turns on safety mode in YouTube as well.
There are controls that you can access. As a parent, having more of those choices is better.