Under the Philippine Family Code, specifically under the provisions governing marriage, paternity and filiation, and the classification of children, the rules concerning legitimated children are crucial. Here’s a comprehensive look at legitimation under Philippine Civil Law, particularly under the Family Code:

1. Definition and Nature of Legitimated Children

Legitimation is the process by which children who are born out of wedlock, and would therefore be considered "illegitimate," acquire the status of legitimacy by virtue of the subsequent marriage of their biological parents. This means that they are given the same rights and status as those born to parents who were married at the time of their birth.
Legitimated children, once the requirements for legitimation are satisfied, are considered in all respects as legitimate. They are thus entitled to the same legal rights and benefits, including inheritance rights, as legitimate children born to parents who were married at the time of conception.

2. Legal Basis and Governing Law

The concept of legitimation is governed by Articles 177 to 182 of the Family Code of the Philippines.
This process is rooted in the principle that the best interest of the child should prevail and that the law should encourage the sanctity and unity of the family by facilitating the recognition and legitimation of children.

3. Requirements for Legitimation

Parents’ Qualification: Only parents who are legally capable of marrying each other at the time of the child’s conception can legitimate their children. This means that if the parents were not disqualified from marriage (e.g., not within prohibited degrees of relationship), legitimation can be granted upon their subsequent marriage.
Child's Birth Status: The child must have been born out of wedlock. Legitimation does not apply to children conceived and born within a valid marriage (who are already legitimate) or to children conceived by parents who cannot marry each other.
Subsequent Valid Marriage: The parents must marry each other after the child’s birth, and this marriage must be valid. This marriage retroactively affects the child’s status and confers upon them the rights and privileges of a legitimate child.

4. Effects of Legitimation

Full Legitimate Status: Once legitimated, the child is considered a legitimate child of both parents for all purposes. They acquire the rights of a legitimate child retroactively from birth.
Inheritance Rights: Legitimated children are entitled to the same inheritance rights as legitimate children. This means they have compulsory shares in the estate of both parents, including rights to legitimate, compulsory, and intestate succession.
Parental Authority and Support: Legitimation allows legitimated children to be entitled to the full exercise of parental authority by both parents. They also have a right to support and, in cases of separation, to participate in custody arrangements.

5. Process of Legitimation

The process of legitimation in the Philippines is not complicated by a formal court proceeding or legal action; rather, it occurs automatically by operation of law when the qualifying conditions (i.e., subsequent marriage of the parents) are met.
Documentation: The legitimated status of the child must, however, be properly recorded in the Civil Registry. The birth certificate of the child should reflect the change in status from illegitimate to legitimate, and the child’s surname may also be updated to reflect the use of the father’s surname.
Civil Registry Requirements: The parents or an authorized representative typically need to file a legitimation form or an affidavit of legitimation with the local Civil Registrar, attaching a copy of the parents’ marriage certificate. The Civil Registrar then annotates the child’s birth certificate to reflect their new status.

6. Rights of Legitimated Children Compared to Legitimate and Illegitimate Children

Legitimated vs. Legitimate Children: Legitimated children, once legitimated, have equal rights to those of legitimate children.
Legitimated vs. Illegitimate Children: Before legitimation, illegitimate children have limited inheritance rights, typically only to the estate of their biological parents with whom they are filiated, and at half the share of legitimate children. After legitimation, these limitations are removed, and they gain the full rights as legitimate children.
In contrast to legitimated children, illegitimate children cannot benefit from the inheritance rights associated with legitimate filiation unless legitimated. Additionally, legitimated children are automatically entitled to use their father’s surname upon legitimation, whereas illegitimate children’s use of the father’s surname generally requires acknowledgment and a specific affidavit.

7. Void Marriages and Legitimation

Legitimation is only possible when the parents’ marriage is valid. If the marriage of the parents is declared void ab initio (from the beginning), legitimation is not effective. This limitation underscores the necessity for a valid and legal union between parents to confer legitimacy to their child.

8. Effects of Annulment or Declaration of Nullity on Legitimated Children

If the marriage between the parents is later annulled or declared void after legitimation, it does not affect the legitimate status of children who were legitimated by that marriage. Their status as legitimated children and their corresponding rights remain intact and are not retroactively affected by the annulment or nullity.

9. Recognition of Legitimation in Special Situations

Adopted Children: Legitimation does not apply to adopted children. Adoption is a separate process conferring similar rights to that of legitimation but does not change the child's natural filiation.
Dual Nationality or International Aspects: Legitimation recognized in the Philippines is also valid under Philippine law when involving Filipino citizens who marry abroad. However, the recognition of legitimation may vary internationally, depending on the laws of other countries.

10. Amendment and Revocation of Legitimation

Legitimation is irrevocable. Once the child is legitimated, the status cannot be undone by any act of the parents. This reinforces the child’s right to stability in their status and relationship with their parents.

11. Relevant Jurisprudence and Case Law

Philippine jurisprudence consistently supports the application of legitimation laws, emphasizing the law's intent to prioritize the child's welfare and ensure they receive equal rights as legitimate children. Court decisions often interpret the requirements for legitimation liberally in favor of the child.

In summary, legitimation in the Philippine Family Code is a legal process that provides children born out of wedlock the chance to acquire legitimate status through the subsequent marriage of their biological parents. This process grants them all rights accorded to legitimate children, supporting the state's policy to protect children’s rights and uphold family unity.