Does a business partnership have to be legally formalized?
That said, business certificates (or business licenses as they are sometimes called) are legal documents. And, while I might be biased, I believe it's good business hygiene to consult with an attorney whenever you are faced with a legal document. In addition, going into business with your son raises a whole host of issues concerning your ownership, management and entitlement to profits from your business.
Without the proper documentation, state laws often contain default provisions that make assumptions--and those assumptions may not match how you want to run your company. Another good reason to have a lawyer on your team.