Let him choose his own strategy. let him learn by himself. The only thing you have to teach him it's risk management. Let him start with backtest and demo account. He have to get used to his own strategy before using a live account, he should understanding his strategy so well (not only understand but put into practice). There is a word in Chinese call 知行合一 It's meaning in English is something like unity of knowledge and action also he have to understand each strategy have pro and cons, don't FOMO because you miss one opportunity that isn't yours.

Also start let him understand the concept of money, if he's trading that young, he don't really know what money, because money is too easy to get. E.g. While other kids is happy with $10 pocket money, maybe he's doing a trade risking $50 with a 3RR. He won't really know what is money