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.