A few links to start:

www.linkopedia.com
Wonderful collection of websites safe for children age 3 to 10.
But since linkopedia does also link to websites not suited for children,
this is not in the default trusted links of Feuersalamander
(you can of course trust linkopedia yourself).

pbskids.org
A safe place for kids to explore and play hundreds of fun educational
games with their favorite PBS KIDS characters.

kids.yahoo.com
Yahoo's kid's pages.

www.askkids.com
A search engine for kids.