The site is ad-free and chock-full of facts, activities, and printables, so there's plenty for kids to do while learning. That said, it's not the most sophisticated site; it lacks a continuity of style, and some of the graphics are a bit simplistic (though some of the printable "comic books" are colorful and pleasing). Plus, some of the content feels wonky, as if it were created by science writers with little kid experience; for instance, does your one- to three-year-old -- the target age range -- really need to know about acid rain?
But, at least the site doesn't talk down to its audience. And, if the presentation lacks sophistication, the information doesn't. Some of the pages are slow to load, a couple of links didn't go anywhere, and the site can be a bit disjointed, but there's some worthwhile content that will get your little ones thinking about their footprint on the earth.