in my experience, this is just a simple introduction. don't worry about asking the right questions or getting a feel for their "interest" yet. you'll know that soon enough. as long as son is polite, shakes hands firmly, makes eye contact during conversation, etc. he'll be fine.
also, these visits are good for your son to watch how the staff interacts with players. make sure to go early and watch bp and warm-up drills. funny story with my son, also class of 2010. after his first visit he looked at me and remarked that he felt like a piece of meat......i laughed i had noticed the same. every coach on the staff shook hands to judge his grip, grabbed his shoulder and eye balled him up and down! he's a little over 6'2" and 205 lbs. it was too funny! hope your son's not shy.......
if son has a true interest in the school for academic reasons, it would be a good time to visit the admissions office, tour the campus, etc.