Seems like there would be lots of stuff. I involve my kids quite a bit in my home office work.
I’d brainstorm all the stuff you could show them then filter that on what THEY are interested in.
And my experience with Interns (and somewhat my kids) is that they are more interested in feeling like they got real work done than it being interesting. YMMV.
They can do usability testing (where they are either the Testee or testOR), maybe your website or one you’re working on. They could do a some tests on UserTesting.com or something similar. This one is great because no expertise is needed, IN fact, you need no-expertise!
Research the answer to a problem (something non technical, maybe tech support kind of thing)…Describe the problem clearly to them and them either let them search or show them where you’d search (and then maybe give them another problem.
Show them your workflow. How a job starts (for contract work) and what kind of problems you try to prevent (clear specs from the user). You must have some good war stories.
Hopefully they’ll have lots of questions. That’s more fun for you an them.