https://www.stem.org.uk/home-learning/primary (also has resources for upper grades)
https://www.nasa.gov/stem-at-home-for-students-k-4.html
https://thestemlaboratory.com/stem-activities-for-kids/
https://www.sciencebuddies.org/stem-activities
https://www.teachengineering.org/#homeschool
https://www.funology.com/funology-science-experiments/
http://www.kidsciencechallenge.com/year-four/teachers_activities.php
http://www.weatherwizkids.com/?page_id=5
https://pbskids.org/designsquad/ (requires creating login)
https://pbskids.org/catinthehat/games/
https://www.msichicago.org/science-at-home/hands-on-science/