I assume there are offline versions of Wikipedia, but anything with content filtered? There are some serial killer pages on there that are pretty NSFL even for adults.
An educational resource for UK school kids. There's a vast amount of content for all ages. Here's an example of explaining programming constructs:
https://www.bbc.co.uk/bitesize/guides/zh66pbk/revision/2
You would need to crawl the site in order to download the content for offline use. I suspect the interactive quizzes won't work in offline mode. Also, modern websites saved for offline use are unlikely to display correctly in a 2007 Web browser.
As an aside: your question is very interesting because no-one makes offline content anymore. Learning resources on CD like Encarta (CD encyclopedia) no longer exist. However, you can probably find old educational CDs on eBay e.g. from The Learning Company - titles are of variable quality.
If your child is very hands-on/project-oriented, set up an IDE/word processor/image manipulation program and let em make stuff.