Maybe.
The starting of the LLC doesn't itself mean much. Since your son is a full-time student under 24, you must meet these other tests to claim him as a Qualifying Child:
-He must not provide more than half of his own financial support. So, if he's making good money, you are probably not providing greater than one half of his support. That being said, his LLC could be bringing in next to nothing...
-He must live with you for more than half the year, or be considered to live with you (i.e. he's away at school, but otherwise your home is his home)
-He must not be married and filing a joint return (this one is a little more complicated, and I'm going to assume it doesn't apply)
If its a single-member LLC, he reports everything on his 1040, Schedule C- just like if he received a 1099MISC. If he has partners, the return filed is a 1065. The income is then split and reported on his 1040 via a K1.
