BBC Bitesize is always free and has videos, lessons, and games covering the whole curriculum all the way up to GCSEs

https://www.bbc.co.uk/bitesize

Oxford Owl provides free ebooks all the time for children of primary age.

https://www.oxfordowl.co.uk/for-home/find-a-book/library-page/

Hungry Little Minds

Short videos and simple, fun activities that you and your children can do together. We’ve broken down the activities by age, but no one knows your child better than you do. So you could pick and choose the ideas that feel right for you, adapt our suggestions or even come up with your own. And you can use whatever language you feel most comfortable with.

https://hungrylittleminds.campaign.gov.uk/