Legal Question in Family Law in California

In order to change your son's last name, you need to file a Petition for Name Change with the Court. This requires you to notify the biological father of your request and to publish your request in the newspaper. Good Luck.

Ms. Chen is not correct if I understand your facts correctly. You can still change your name just based on the marriage, but you would need a court order to change the child's name. If, however, his biological father is not his legal father, which I assume he is not since he is not on the birth certificate, then he has no say in the matter. If, however, for some reason he has established legal paternity but is not on the birth certificate (not sure how or why that would be) then she is right that he would have to be notified and given an opportunity to intervene.