What could be the best way to introduce the world of computers to a kid, let’s say of 6 years old, so that he learns to handle it like a toy and stops dreading it like some esoteric, arcane and recondite machine from some eldritch, enigmatic, cryptic and phantasmal world ?
You pretty much had the answer in the query there is think. Just present it as toy to be handled.
To get more into detail, you probably would prefer those you can indeed pull apart and handle like toys than the “modern” slick ones. I see people mentioning raspberry pi. It’s hard to fear it looking at its guts with bare eyes. After they fried a few chips pressing soldering iron for too long they will have zero respect for electrical computers.