What resources can you recommend that are in-depth and age-appropriate? I'd be open to college-level textbook recommendations.
Another is give them a old PC or laptop with a blanked HDD and a distro disk/usb (or balank medium and instruct them to choose one on distrowatch) and let them a taste of setting up a system.
EdX has a bunch of college level CS courses, including several verions of Harvard's CS50 courses. Start with Introduction to CS. Free to audit.
Most top CS schools (Stanford, MIT, CMU) have some sort of online lectures. There's also always Udacity/edx as well.