NoveList K-8 contains information about books for children from kindergarten to grade 8, including picture books, chapter books, and young adult novels.
Oxford English Dictionary
The OED is the world's most complete dictionary.
TumbleBooks is the place to go for animated storybooks and other literacy-related activities.
World Book Kids
World Book Kids includes thousands of easy-to-read articles, images, interactive games and activities, and teacher resources.