It seems to me that some areas are weaker online for young learners... especially Science and History.
Science
Webcams
http://nationalzoo.si.edu/Animals/WebCams/
YouTube and TeacherTube also have some resources, if carefully managed.
Tinkering with Ideas
http://www.inventionatplay.org/playhouse_tinker.html
History
http://www.bbc.co.uk/schools/barnabybear/games/changed.shtml