Mystery Science
https://mysteryscience.com
Free science lessons.

STEM learning

https://www.stem.org.uk/primary-science
Free science resources and activities to support the National Curriculum for Science.

Crest Awards
https://www.crestawards.org
Science awards you can complete from home.

Science Bob

https://sciencebob.com/

This has some interesting experiments which can be done at home using only everyday kitchen items. It also explains the science behind each experiment.