Child-Friendly Search Engines and Image Sites
Be aware that NOTHING on the Internet is guaranteed - inappropriate images or information can appear in the most unlikely spots. Teach the kids to always let you know if they run across something that makes them feel uncomfortable and you can deal with it in the age appropriate fashion.
Here are a few search engines and image sites that are for kids. Some are more general and some for a more specific purpose.
Ask Kids
Kids Click
Yahoo Kids
CyberSleuth Kids
Fact Monster
BBC
http://www.bbc.co.uk/cbbc/find/
Ithaki for Kids
How Stuff Works
Creative Commons
Pics 4 Learning
Tag Galaxy
http://taggalaxy.de/ (not especially for kids, but it does help the child narrow his search)