Here are some more kids stuff I've seen (sometimes with different reader UX from the above):

1/ Global Digital Library (PDF and ePub format) https://digitallibrary.io/ and as offline-capable Kolibri channel https://kolibri-catalog-en.learningequality.org/en/learn/#/t...

2/ Pratham Books' StoryWeaver (includes some of the African Storybook titles, and based around PDFs) https://kolibri-demo.learningequality.org/en/learn/#/topics/...

3/ Learn JS games (probably need 6+ years old for this) https://kolibri-catalog-en.learningequality.org/en/learn/#/t...

4/ Videos of kids from different cultures: https://kolibri-catalog-en.learningequality.org/en/learn/#/t...

5/ Educational math videos with lots of singing: https://kolibri-catalog-en.learningequality.org/en/learn/#/t...

And more generally, you can see all EN channels in the catalog: https://catalog.learningequality.org/#/public?languages=en