Go to your civil registry and apply for changing of your baby's name on all documents submitted to them (birth certificate, et.al.). Get a lawyer. A court hearing will then follow for the judge to approve the request for changing names. Go to foreign affairs and present the approval from judge and apply for new passport. Apply for a new RP for your baby. It will take minimum of 2 months, depending on availability of court, plus money to change all legal documents.