http://www.hsbaseballweb.com/pro-scouting/agents_vs_advisors.htmWelcome to the HSBBW.
As a parent that has gone through the process, I feel that it is not necessary to deal with an advisor at this time unless your son is projected in the top rounds. If your son is drafted, then he may need an agent.
What you should do, is become familiar with the draft process and what is called "slot money". And familiarize yourself with what an advisor or agent does or doesnot do. Many HS students generate interest, that means they are good. It is an exciting time, and confusing time. You must be very careful who you speak to as you wouldnot want to jeopardize any eligibilty if your son has committed to a college.
Most big companies only represent the top prospects and some will only represent college players. All players sign a minor league contract, only a few lucky players actually sign MLB contracts out of HS or college. As the season approaches and your son begins to play, yu get closer to the draft, things will become clearer. Just do your homework first, be prepared.
If you have any specific questions you can go to the main board and read, there have been many discussions about advisors/agents.
Best of luck to your son.