Yes, time once passed cannot be reclaimed…and that includes your kid being a kid.
You sound like you want your son to study in the U.S. Many students…engineering students included, have interests other than engineering which they bring to the college admissions process. Please remember that if your kiddo comes here, he will meet others his age with interests other than academic ones. You want him to have good interaction and social skills too…and things he can do to unwind.
My engineering major was a musician also, and a swimmer. To relax, she played in the college orchestra…and went to the fitness center and swam. It wasn’t all about engineering 24/7.
It sounds like your 12 or so year old really loves science and math. But really…unless he spends a week or so shadowing an engineer, I can’t imagine how he would KNOW for sure that this is what he wants to do forever. And beside that…there are many different kinds of engineering.
He could change his mind if he is allowed to,explore other areas.
And he might change his mind when he gets to college. The vast majority of college students here DO switch majors.