My son went to headfirst and Stanford after soph year - and same camps after Jr yr. The connections he made during the soph yr camps really helped for the Jr yr camps. While the coaches are not actively looking for rising jrs, they will remember you. It is no risk to you - except expense - to go after soph yr.
Coaches know that physically you will really grow between those years, so the fact that you're small or light and don't throw as hard as kids a year older makes no difference.
Be enthusiastic, play the game hard, have your transcript and a short note about youself sealed in a bunch of envelopes and give them to coaches who speak to you. And, speak to the coaches by yourself - without your parents. Do some research on the schools that will be there so you have a feel for which schools interest you (big, little, near, far, etc.) And you can carry on a brief conversation. Coaches want to begin to get to know you - your parents are not part of the equation.
The coaches will always ask you about your grades, your scores (if you haven't taken the SAT or ACT then they'll ask about your PSAT), and your courses - beacuse that is what they care about!