A method of developing Web3d-based children's education software is presented, on the basis of constructivism for learning, children like to learn knowledge in entertainment manner, and 3D virtual environment is suitable for children's exploration. The method is illustrated with three examples, the first is a virtual observation experiment for sun, users can handle a virtual telescope to watch a virtual sun's images and learning sun knowledge in an interactive manner; the second is a virtual park, users can roam in a virtual natural landscape; the third is a virtual aquarium, users can watch a lot of fishes from different viewpoints. These examples show that Web3d technology has powerful functions in developing children's e-learning software.