Below are tips on enabling safety search filters(adult content) for the major search engines:

AllTheWeb: Use the Basic Settings page to enable the Offensive Content Filter option. The only works for searches in English.

AltaVista: Use the Family Filter Setup page.

AOL Search: Doesn't appear to offer a filter, but enabling Parental Controls might have an impact on web search matches.

Ask Jeeves: Use options for Content Filtering on the Your Settings page or try Ask Jeeves For Kids, http://www.ajkids.com/.

Google: See the SafeSearch help page for instructions on setting up filtering on a permanent or as-needed basis.

HotBot: Use the Block Offensive Content section of the Filter Preferences page. Note that you may need to set this again if you change from using the default "HotBot" search engine that's offered.

Lycos: Use the Adult Filter section of the Advanced Search Filters page.

MSN Search: Use the Safe Search Filter on the Settings page.

Teoma: Teoma doesn't appear to offer a filter.

Yahoo: Set the SafeSearch Filter option via the Search Preferences page.