PebbleGo is a picture-based encyclopedia database that is easy (and fun) for students in Kindergarten to Third Grade or higher! Animals and Dinosaurs.
PebbleGo Next is geared towards students in grades 3-5. Biographies, States, and Native Americans.
Both have text-to-speech, glossaries, videos and related games.
Other Research Sites Online
Ducksters - Ducksters can be a place to start your research in History, Geography, Science, and Biographies.
Kiddle - Kiddle search results are filtered and aimed at kids!
SweetSearch - Sweet Search uses librarian- and educator-chosen sites to find the best results for student research needs, faster!