I've taught a lot of "kids" a lot of things, including reloading, whether literal kids or the colloquial signifying teen to early 30 something "kids." Obviously, nobody is condoning anyone allow an 8 year old to charge cases independently, but there are plenty of operations kids can be trusted to complete, and which can be safe for a kid (depriming with nitrile gloves, hand washing, safety glasses, pinch shields, for example).
I'm no longer current, but I've taught the NRA Metallic Reloading course in the past, as well as one-on-one and small group instruction classes and coaching. Personally, I have seen a considerable increase in interest in reloading in the last ~10yrs. Whether for an interest in prepping, attempts to get in front of political upheaval, high volume AR blasting, or long range precision shooting (or not so long), it seems there's been a massive growth in interest in recent years.
Teaching reloading to a child isn't so different than teaching anything else to a child. The duration should be commensurate with the ability of the child to sustain diligent focus, and the risks assumed in terms of process safety and product quality (safety as well) need to be thoroughly understood before introducing the kids.