The answer depends on whether you want to insure your son to drive your car or insure his car on your policy. You may be able to insure him as a driver on your policy by contacting your insurance company to determine their procedure and guidelines and this type of coverage and if there would be any additional premium due.
If you want to insure his car on your policy you will need to check with your insurance company as some of them will not insure vehicles from more than one household on a single policy. This might not apply if he is a student and keeping his car away at school.
If your son owns his own car and house than typically he would have to obtain his own car insurance and could no longer be kept on your insurance policy since he is out of your household and thus his vehicle is garaged at a different location.