Below are the links to lots of useful websites which children can use.
Especially good for maths and computing for all ages but other subjects at Secondary level. Note this uses the U.S. grade system but it's mostly common material.
This site is old and no longer updated and yet there's so much still available, from language learning to BBC Bitesize for revision. No TV licence required except for content on BBC iPlayer.
Learn computer programming skills - fun and free.
Creative computer programming
All sorts of engaging educational videos
National Geographic Kids
Activities and quizzes.
Learn languages for free. Web or app.
Free science lessons
The Kids Should See This
Wide range of cool educational videos
Crash Course Kids
As above for a younger audience
Science awards you can complete from home.
Paw Print Badges
Free challenge packs and other downloads. Many activities can be completed indoors. Badges cost but are optional.
All kinds of making.
Is in U.S. grades, but good for UK Primary age.
A lot of these can be done in a garden, or if you can get to a remote forest location!
Resources for English language learning
Oxford Owl for Home
Lots of free resources for Primary age
Blue Peter Badges
If you have a stamp and a nearby post box.
The Artful Parent
Good, free art activities
Educational online games
DK Find Out
Activities and quizzes
This is more for printouts, and usually at a fee, but they are offering a month of free access to parents.
(Australian but goes in chronological order with free online games eyfs to y6)