In our household, we spend a lot of time doing hands on learning, supplemented by complementary reading. Our bibliography reflects this style.
The KidZone site is targeted to the Kindergarten thru Grade Six age group. Much of the basic information on the site is knowledge accumulated through the years and is known by most adults (information like "birds have feathers") -- I can't give a specific bibliography for this type of information (other than a big thank-you to all the great teachers I had in my young life and the equally wonderful teachers my daughters Tasha and Kaitlyn have now).
Most of the specific animal and plant information has been shared with us by the helpful staff at the Calgary Zoo, Seaworld, Disney's Animal Kingdom, Canadian National Parks and US National Parks during talks with guides and from informational signs posted.
Many of the science section items (planets, science experiments, etc) have been learned at the Calgary Science Center during the various presentations they have given.