Not much more to add since 9and7dad nailed it. JoeMktg son was drafted out of high school. PM him. I have found him responsive to draft questions.
"This isn't about money".....but it will eventually come down to that. If your son does get drafted, you will have to weigh out the cost/benefit of signing as a HS player. Yes, college could be paid for with the MLB scholarship, which could be important to some, but there is a lot of benefit to going to college. Including getting drafted later at a higher round. (Getting drafted at a higher round is more than just the money. HS players and high rounders ARE treated differently...unless you are a high round HS player.)
He can turn down the offer if drafted. Many do.
Sometimes teams will draft a HS player (or college for that matter) on the third day with low money just to use up a slot, hoping he won't sign. But , he will be on the radar, PG will list his draft status on his PG profile, etc. College coaches have been known to up the scholarship to keep players from entering the draft.