What are your rights when a notary has willingly notarized a legal document concerning your son's inheritance and excluding him from the heirs?

You have no rights against a notary. A notary simply certifies that the people who signed the document where the people they said they were and/or that they made the statement or document they are signing. The person you need to talk with is the person who created the document in the first place that is dis-inheriting him. The drafter of the document is who you want.