Always remember that image searching can never be 100% safe, so always proceed with caution - Google Safe Images purports to offer safe image searching, but should never be used without close supervision. The only site I would be entirely confident about is pics4learning.com.
Away from the corporate search tools, other specific tools for children include:
- BBC - not the full search engine of the past, but a useful tool which provides categorised links to BBC content plus a few links from 'elsewhere on the web';
- KidsClick and DidDabDoo - US-based sites, which are browsable indexes, like the old Yahoo, which provide relatively short lists of appropriate web sites in response to search terms;
- Been a while since its been updated, but the Searchbox Children's page brings together a full range of child-friendly search engines on one useful page.