The AAP website is a great resource for information on various aspects of child health including immunizations and safety/injury prevention (including car seats, product recalls), as well as lots of family education information.
The CDC website is an excellent source of information regarding immunizations, especially the "travel" section which gives updated travel alerts and recommended immunizations/medications for visits outside the United States (Example: "Should my teenager receive the Hepatitis A vaccine if we are traveling to Southeast Asia?")