minivamom- Nothing wrong with being proactive. Any form of contact is good, visits are great. If your son is interested in the schools that have been pursuing him, then definitely have him contact them on a consistent basis. Make sure they understand his interest level and stay on him. Recruiting is a two-way street many times in college baseball, and I think you'd be surprised to hear how many times persistence from a player turns out successful.
No need to stress, your son sounds like he is in a very favorable position. Absolutely a good idea to call if he is interested in pursuing these schools.
One note, make sure your son is the one doing the contacting, whether it be via email or phone. The coaches are recruiting young men, they want to see the responsibility