It depends.
The first rule is, if your son files a joint return with his wife, or if he has a dependent child of his own, you don't claim him as a dependent.
If your son doesn't have income and won't file his own tax return, or will file as married filing separately, then he could be claimed as a dependent if he meets the usual rules (lived with you more than half the year, did not provide more than half his own support).
However, you would receive at most a $500 tax credit, and asking your son and his wife to both file married filing separately could cost them more than $500 in higher taxes.
