I agree, at that age interests change frequently.
Boy, do I agree with this. From about age 5, my son obsessed over being a pilot. At age 12, he joined CAP and has thrived in the program (currently about to promote to c/lt colonel, has been squadron leader for over a year, and hopes to have his Spaatz award before he graduates.). Also decided AFA was the path for him at 12 and began a relationship with our local congressman. He was so steadfast in this goal, we planned our course of action around this dream. We let him take the lead in this. He went to 2 glider encampments, tons of leadership encampments (including serving as staff), has been at the top of his class since 7th grade, done countless hours of community service, etc. He has really put in the effort to make this happen. Then, last summer, he went to his powered flight academy and came back and immediately announced a COMPLETE change of heart on his goals. I still don't know if it was something that happened at that flight academy (he denies it), or if he just truly lost interest in flying, but, now, all of a sudden, he wants to go into astrophysics. No less a lofty goal, mind you, but it has required us to shift our thinking and focus a bit. We were a little rattled, but we want him to be happy, so we have begun carving out a new course of action.
Thankfully, that new goal still includes AFA or AFROTC (Plan B), and, lately, he has decided it would be prudent to go ahead and apply for USNA as well, to further "hedge his bets." He is attending Summer Seminar next week, where we feel his mind will most likely be made up for sure, one way or another, if AFA is the path he wants to stay on. Assuming he receives and accepts an appointment, it's always possible he could get there and decide on a completely DIFFERENT career path, once he starts classes! My point is that the greatest lesson we have learned through this, as parents, is to "roll with the punches" and keep encouraging our DS to aspire to be the best he can be, no matter what that may be. He is well on his way. I wish you and your children all the best in the upcoming decisions over their life choices!