In the Philippine legal system, the process of changing a child’s surname from the mother’s to the father’s following the subsequent marriage of the parents is known as Legitimation. This is a legal remedy that elevates the status of a child born out of wedlock to that of a legitimate child, granting them the same rights and privileges as children conceived during marriage.

1. Legal Basis for Legitimation

The primary laws governing legitimation are the Family Code of the Philippines (Articles 177 to 182) and Republic Act No. 9858, which amended the Family Code to expand the scope of who can be legitimated.

Under these laws, legitimation takes place by the subsequent valid marriage between the child's biological parents. However, specific criteria must be met:

Status at Birth: The child must be born outside of wedlock (illegitimate).
Capacity to Marry: At the time the child was conceived, the parents must not have had any legal impediment to marry each other.
The Exception (RA 9858): Previously, if parents were disqualified from marrying due to age, the child could not be legitimated. Under RA 9858, children born to parents who were disqualified only because they were underage (below 18) can now be legitimated, provided the parents eventually marry.

2. The Process of Legitimation

Legitimation does not happen automatically upon the signing of a marriage contract. It requires a formal administrative process through the Local Civil Registry Office (LCRO) where the child’s birth was originally registered.

Step 1: Execution of the Affidavit of Legitimation

The parents must execute an Affidavit of Legitimation. This document must be:

Signed by both parents.
Duly notarized.
Clearly state the names of the parents, the date and place of their marriage, and the fact that they wish to legitimate the child.

Step 2: Registration at the LCRO

The parents must submit the affidavit and supporting documents to the LCRO where the child's birth was recorded. If the child was born abroad, the documents are processed through the Philippine Consulate or the City Civil Registrar of Manila.

Step 3: Annotation of the Birth Certificate

The Local Civil Registrar will not issue a "new" birth certificate in the sense of deleting the old one. Instead, they will annotate the original Birth Certificate. The annotation will state that the child is now legitimated by virtue of the parents' marriage.

Step 4: Verification by the Philippine Statistics Authority (PSA)

Once the LCRO processes the request, the records are forwarded to the PSA. Parents can then request a certified true copy of the birth certificate that reflects the child’s new surname and the legitimation status.

3. Required Documents

To initiate the change, the following documents are typically required:

Original Certificate of Live Birth (of the child).
Certified True Copy of the Marriage Contract (of the parents).
Affidavit of Legitimation (executed by both parents).
Certificate of No Marriage (CENOMAR) of both parents (to prove no legal impediments existed at the time of conception).
Valid IDs of the parents.

4. Effects of Legitimation

Once the process is complete, the child enjoys several legal shifts in status:

Surname: The child’s surname is legally changed to that of the father.
Succession: The child gains the same hereditary rights as a legitimate child (e.g., a full share of the legitime/inheritance).
Support: The child is entitled to the same level of legal support from both parents.
Parental Authority: Both parents now exercise joint parental authority over the child.

5. Important Distinctions

Legitimation vs. RA 9255

It is important to distinguish legitimation from Republic Act No. 9255 (The Law Allowing Illegitimate Children to Use the Surname of their Father).

RA 9255 allows an illegitimate child to use the father's surname if the father recognizes paternity (via an Affidavit of Admission of Paternity), but the child’s status remains illegitimate.
Legitimation requires marriage and changes the child's status to legitimate.

When Legitimation is Not Possible

If the parents were disqualified from marrying at the time of conception (for example, one parent was still legally married to someone else), the child cannot be legitimated. In such cases, the child remains illegitimate, but may still use the father's surname through RA 9255, provided the father acknowledges the child. However, the status on the birth certificate will remain "Illegitimate."

6. Retroactive Effect

The effects of legitimation shall retroact to the time of the child's birth. This means that for all legal intents and purposes, the child is treated as if they were born within a valid marriage from the very beginning.

How old is the child currently, and has the father already signed the birth certificate's "Admission of Paternity" section?