Start early, I guess.
Those are not stem toys. Stem toys are broken bicycles, lawnmowers, tractors, an old truck, a welder, a lathe, a mill and a job building things.
Having little or no money and a desire for things you don’t have and can’t get other than to fix or build them helps too.
I don’t know what it takes to be an electrical or chemical engineer. I never have really figured out what makes those guys tick.