The basic principles are not a great mystery; actually implementing them is hard though. The best ways we know take a lot of time and dedication (e.g. hours per day of 1:1 or 1:few full-attention effort from an adult tutor who is both a subject expert and an expert teacher), more than we’re usually willing or able to spend on a child. Take a look at the Polgar sisters.
The Polgar sisters are not geniuses in any general sense of that word.
Interesting enough as that "experiment" may have been, it only proved that certain persons of a certain background that includes genetic history unknown to us, can reach high degrees of competence in one __specialized__ field. Chess is also particularly well-coordinated with years of repetitive practice and dedication, but genius? I think not.
You could replace chess with playing the piano even, and the outcome would be the same.
After having interacted with many people who were called “geniuses” in various settings (e.g. Nobel Prize winners, Fields medalists, best-selling novelists, at least a half dozen MacArthur “genius” grant recipients ...), I don’t consider “genius in any general sense” to be a real thing. YMMV.
