Homemade electromagnet safety
What a wonderful time to be able to teach SAFETY,  not only to your 10 year old, but to all of his classmates.  Safety is always on topic here on EE SE.

Children are enamoured with magnetism, and displays of fireworks, and squished things.  

Think this through VERY carefully.  Consider the implications of a magnetism demonstration that builds upon safety.  

And of course with the admonition of "ONLY UPON ADULT SUPERVISION".  

Use the other comments and answers to guide you.   

Then demonstrate how a grape can be squished (like a human's finger).   

No worry's about radiation