https://www.twinkl.co.uk/ - a huge range of different subjects and focuses, arguably the best host of any resource you could need. Have offered a free account in the result of school closures.
https://www.bbc.co.uk/bitesize - huge range of different resources and information broken down into Key Stages and year groups.
https://www.topmarks.co.uk/ - huge treasure trove of activities that cover a whole range of subjects. Also holds links to games etc that are hosted by other sites.
https://spellingframe.co.uk/ - spelling activities with specialist resources for each year group.
https://tpet.co.uk/ - free online resource packs.
https://www.worldbookday.com/world-of-stories/ - lots of free stories to access.
https://imoves.com/the-imovement - a free resources to keep your children active while learning.