Legends of Learning is an engaging set of science games and online activities designed for students in grades 3-8. The system is designed for classroom use, but could be adapted to family use. It features lots of content that is aligned with the NGSS (Next Generation Science Standards).
CK-12 offers a comprehensive system of review resources and practice questions that will help students get ahead in school. The app does a thorough job of covering vital ideas in elementary math as well as middle and high school high school math and science.
Rough Science provides basic introductory information about layers of the earth, states of matter, and adaptation/evolution in the form of a video tutorial and a hands-on challenge that reinforces a simple concept from the video.