Son, age 13, wanted a theremin. My dad is a classical electrical engineer, who grew up pulling apart vacuum tube radios.
I made Son call Dad a month before vacation.
Dad found the schematic for the minimum theremin. He had Son redraw it, replacing logic gates of one type with the type he had on hand. (Yes, Dad has logic gates on hand.) Then he reviewed Son’s soldering skills, helped fine-tune them, and turned him loose with a bunch of parts, including a resistor colour-code chart and a magnifying glass. They used an oscilloscope to track down stray oscillations, removed an unnecessary bit of the circuit, added a filter, and added a diode to save the device in case the user puts the battery in backwards.
Unlike my one-and-only electronics course, they did all this without a single derivative or integral. They used a calculator once, to find the current, V=IR. (Dad could only find his HP, with Reverse Polish Notation. Son learned.)
I’m proud, and a bit jealous.
Daughter, age 10, spent her Grandpa time fishing. She caught more fish than he did. She also arranged a photo-shoot with a 3D puzzle.