The simple answer is that you cannot transfer anything concerning an automobile accident after the fact. Liability, if any, for an accident lies with the owner of the motor vehicle and its driver on the day of the accident. The insurance company that had a policy that was in effect on that date negotiates any settlement, pays any damages, and provides legal counsel if necessary.
The fact that you transferred title to the car after the accident is irrelevant to any legal action or claim for damages. Likewise, changing insurance policies has no effect. As owner of the vehicle at the time of the accident, you are going to be involved in any litigation.
Hopefully, you have delivered any legal papers to the insurance company that had the policy on the date of the accident. They will take care of everything from that point forward. They will, of course, need to speak with you and your son.
The insurance company will hire an attorney to appear on your behalf. Remember, though, that the attorney is really representing the insurance company. If the civil action is seeking more money than the limits of your insurance company, then you probably should at least speak with a California attorney about your possible liability for damages beyond your coverage limits.