It's certainly out there. If not wish to come across it of course using keyword filters goes a long way to blocking most out of search results. Keyword & extension filter words to Add also blocks out a certain % of the general spam, porn, etc. depending on how much you wish to filter out.

If child porn is out there, there is also obviously a demand for it, which is sad but a fact of life. O.o Trying to reduce the demand would help of course, however that can be done.