In the Philippine legal system, legitimation is a process by which children conceived and born outside of wedlock are considered legitimate by the subsequent valid marriage of their parents. Under the Family Code of the Philippines and Republic Act No. 9858, this process allows for the correction of a child’s status and the updating of their birth records to reflect the legal benefits of legitimacy.

1. Requirements for Legitimation

Not all children born outside of marriage are eligible for legitimation. The following conditions must be met:

Status at Conception: At the time the child was conceived, the parents must not have been disqualified by any legal impediment to marry each other (or, under R.A. 9858, if the parents were disqualified due to age, they may still legitimate the child upon marriage).
Subsequent Marriage: The parents must enter into a valid marriage after the child's birth.
Acknowledgement: The father must have acknowledged the child, either through the birth certificate or a separate public document/private handwritten instrument.

2. Essential Documents

To update the birth records at the Local Civil Registry (LCR) and subsequently the Philippine Statistics Authority (PSA), the following documents are typically required:

Certified True Copy (CTC) of the Certificate of Live Birth (COLB): The original record currently on file.
Certified True Copy of the Marriage Certificate: Proving the subsequent marriage of the parents.
Affidavit of Legitimation: An omnibus sworn statement executed by both parents asserting the facts of the birth, the lack of legal impediment to marry at the time of conception, and the fact of their subsequent marriage.
CENOMAR (Certificate of No Marriage): Of both parents, to verify there were no prior conflicting marriages.
Acknowledgment of Paternity: If the father did not sign the original birth certificate, a separate private handwritten instrument or "Affidavit of Admission of Paternity" is required.

3. The Step-by-Step Process

Step 1: Filing with the Local Civil Registrar (LCR)

The parents must file the Affidavit of Legitimation and supporting documents with the LCR of the city or municipality where the child was born. If the birth occurred abroad, the documents are filed with the Philippine Consulate or Embassy having jurisdiction, which will then forward them to the Department of Foreign Affairs and the PSA.

Step 2: Registration and Annotation

The LCR will examine the documents for authenticity. Once approved, the LCR will not issue a "new" birth certificate in the sense of destroying the old one. Instead, they will annotate the existing birth certificate.

Note: The annotation will state that the child is now legitimated by virtue of the marriage of the parents on a specific date and that the child shall henceforth use the surname of the father.

Step 3: Endorsement to the PSA

After the LCR has recorded the legitimation, the Local Civil Registrar will endorse the annotated record to the Philippine Statistics Authority (PSA) in Quezon City. This ensures that the national database is updated.

Step 4: Requesting the Annotated COLB

After a processing period (usually several months), the parents or the child may request a copy of the Birth Certificate on PSA security paper. This copy will feature the marginal annotation confirming the legitimation.

4. Legal Effects of the Update

Once the records are updated, the child gains the following legal rights:

Surname: The child is entitled to use the surname of the father as a matter of right.
Succession: The child gains the same hereditary rights (legitime) as a legitimate child born during marriage.
Support: The child is entitled to full legal support from both parents.

5. Important Considerations

Legitimation vs. Adoption: Legitimation is only possible for the natural parents of the child. If a step-parent wishes to grant a child legitimate status, the process required is Adoption, not legitimation.
Rule on "Already Legitimate": If the parents were married at the time of conception or birth, the child is already legitimate. If the birth was mistakenly registered as "illegitimate," the remedy is a Petition for Correction of Clerical Error or a judicial proceeding, depending on the gravity of the error.
Processing Time: While the LCR process can be completed in a few weeks, the synchronization with the PSA database often takes four to six months.