Start laughing when they start talking.
NOT being represented by counsel is a serious mistake. They will probably offer you $1,000-$1,500 plus medical, each. You owe it to yourself and to your son to seek advice of a local personal injury attorney.
There is no generic answer to your question, for it depends upon the locality where you live or where a claim would be brought. In some states which have no-fault statutes providing for medical care and lost wages, among other things, whiplash injuries are considered soft tissue injuries and not severe enough to permit someone to bring a suit.
Speak to someone who practices where you live and who regularly handles these types of cases.
Disclaimer: Mr. Milligram is an attorney licensed to practice law in the States of New York and New Jersey. This response is not legal advice and does not create an attorney/client relationship; rather this response is intended to be legal education only and is intended to provide general information about the matter in question. Please note that this answer does not constitute legal advice. It is merely intended to provide educational material and general information to aid the poster in finding answers to the problem posed. This answer does not create an attorney-client relationship. In most cases, it is best to contact an attorney directly to find answers to your problems.
What is the average settlement for whiplash? There is no real answer to your question, because there is no typical case or amount. The fact that you have PTSD symptoms, which often require treatment over a lengthy period of time, means that it’s impossible to give you an idea what those cost factors might be at this juncture.
You should obtain needed medical care and treatment immediately and follow the doctor's advice. Do not give any statement to the adverse party or insurance company; nor should you grant them access to any medical records. Photograph the injuries and the damage done to any property. Contact a personal injury attorney in your area as soon as possible so that you can protect your rights.
You may also find it helpful to review the Legal Guides I have published on Avvo.com dealing with many of the issues you are now facing.