Hi Kathi,
This sounds somewhat like existential anxiety to me, but I'm not a psychologist. Exisential anxiety is not uncommon for highly intelligent kids, especially the young philosopher. I really don't have any good ideas for you except maybe google existential anxiety kids and see if the descriptions sound like your son.
You could find a child psychologist who tests for giftedness and is practiced in these types of issues. You mentioned your daughter would like to go to Wheaton college. If you live anywhere near Wheaton, I know a Psyd. that specializes in child/gifted and he is the best in the area. Feel free to private message me for his name.
Peace,
Incog
