If you go to ask.com and type some queries, you'll get this message: "This query does not comply with Ask.com Terms of Service".
Here's a list of some queries that return this message:
sexy girls
Belgium's laws on pedophilia
laws on pedophilia
sex with kids
sex of a child
pedophilia
anti-pedophilia
child sex abuse
zoophilia
blocking porn from kids
any query that contains child and sex, kids and sex
I think this is not a good idea: those who want to search for these things will go to another search engine. Besides, some people may just want to make some research on "laws on pedophilia". If you ban queries like that, you'll have to ban others: "how to make a bomb", terrorists or "suicide tips" and the list will never end.
Update: If you search for "pedaphilia", Ask suggests searches like "girl love pedophilia", "child porn", and "preteen girl virgin".
{June 27 update} Here's Gary Price's response:
It's really a legacy issue from the Ask Jeeves days. Much of it having to do with the one time licensing agreement between our company and the "Mr Jeeves" Woodhouse licensing organization. It was far from an ideal situation and far from perfect filtering.
The good news is that with Mr. Jeeves gone, these issues no longer apply. So, as Lanzone pointed out earlier, you'll see big changes beginning later this week.
Actually, changes have been developing for a few months. Here's an example.
Shortly after I started working at Ask.com (in March) a librarian colleague sent me a note asking why her organization and other info about a topic wasn't found in Ask. These terms were on what we'll call the "legacy" list of filtered terms. It was not a long list. When I was alerted to this problem I immediately contacted Ask.com management and the terms were searchable within a matter of days. Now, as we move forward, this issue is being resolved (as Jim points out).
Also see:
Google sued for promoting child pornography