There are a few things to think about. Let's break it down.
- What kind of business does your son have?
- If the vehicle is a part of the business, he could need commercial or business-use insurance. This means he would need an entirely new policy than you as I assume you have a personal lines policy. These policies tend to be more expensive.
- Does your son live with you?
- A lot of insurance companies do not like to cover drivers who don't live in residence because of the risk. They want to insure a vehicle for the location it is parked at the majority of the time.
- You can be financially responsible for the damage
- If your son gets into an at-fault accident and the value of damage exceed the limits of the policy, you can be financially responsible for the reminder. If you do go ahead with getting your son the policy, I highly recommend getting the highest available liability limits. 100/300/100, at least. Otherwise, you and your wife put your assets at risk.
Your best bet is to speak to the insurance agent at your company.