I received some questions by private message, and I think the answers will be of general interest, so here goes:
1) Is it OK for freshmen to go?
Yes, that is fine. My son tagged along with me one time when I was really doing my personal research, and not expecting him to do anything but look around. He was sixth-grade age at the time, and was treated very politely by representatives of a famous college at the college fair I attended that day. They invited him and me to attend a regional information session later that school year, the first I ever attended.
2) Whatever you normally wear to school is appropriate dress; I certainly see high school students who look like regular high school students at most college information sessions I attend.
3) If they wind up speaking with someone, is their contact "tracked"?
It may or may not be, depending on the college. If the conversation begins with "I'm a freshman, and I'm just getting an early start looking around," that shouldn't be off-putting if the student is young and acts younger than a senior.
4) It is a good idea for the student to have a personal email address that looks serious, for example
jsmith@isp.com
rather than
hotpartyingbabe@aol.com
or whatever it is that teens do these days to try to be funny with email addresses.
I hope that helps. Just being your own polite self and asking reasonably informed questions should go a long way toward gaining information and making a (possibly remembered, possibly not) good impression.