The National Museum of Mathematics offers online sessions, some recurring regularly, for people of all ages, including some designed for senior citizens.
MOS at Home comes from the Boston Museum of Science. They offer videos, podcasts, and activities as well as virtual exhibits.
From the Jet Propulsion Laboratory, this is a page with activities grouped by grade level along with videos and links to other NASA resources.
The Smithsonian Science Education Center has developed STEM resources to support distance Learning needs for students in grades K-8. The site is designed for everyone—students, teachers, and caregivers. It includes standards-aligned educational games, simulations, videos, eBooks, and hands-on lessons that require simple materials found at home. Some resources require technology. Others can be printed out and used in low-tech environments.
Science from Scientists offers lessons and other resources created by trained scientists. Their homeschool workshops are inactive during the Covid pandemic, however families may wish to keep track of this resource for when it reopens.
Resources for families and students to learn at home, for pre-school through high school in many subject areas.
Figure This! is a resource from the National Council of Teachers of Mathematics that provides interesting math challenges that middle-school students can do at home with their families.
Learning Trajectories is a program based at the University of Denver. They provide activities that guide children through successive levels of development in their mathematical thinking.
A brief introduction to STEM learning resources from Bright Horizons. This is a good starting place for ideas.