https://worldbook.kitaboo.com/ is free at the moment and provides access to a wide range of ebooks. It seems particularly useful for setting non-fiction texts to read alongside a Science or Learning Enquiry unit. Thanks to Laura for finding this resource.
https://learnenglishkids.britishcouncil.org/grammar-vocabulary The British Council has a range of English activities. They are mostly aimed at younger years. There are grammar games and spelling activities. The 'listen and watch' section has short stories, poems etc. You could set a story and add some comprehension questions as a quiz on DB for children to respond to.