Who are considered as legitimate children?

1. Children conceived or born during the marriage of the parents are legitimate. 

2. Children conceived as a result of artificial insemination of the wife with the sperm of the husband or that of a donor or both are likewise legitimate children of the husband and his wife, provided, that both of them authorized or ratified such insemination in a written instrument executed and signed by them before the birth of the child. The instrument shall be recorded in the civil registry together with the birth certificate of the child. (Art. 164, Family Code)

3. Children conceived or born before the judgment of annulment has become final and executory shall be considered legitimate (Art. 54, Family Code). This is because voidable or annullable marriages are valid until annulled. 

4. Children conceived or born before the judgment of absolute nullity of the marriage under Article 36 [on the ground of psychological incapacity] shall be considered legitimate (Art. 54, Family Code).

5. Under Art. 42 of the Family Code, the marriage subsequent to the declaration of presumptive death of the absent spouse shall be automatically terminated by the recording of the affidavit of reappearance of the absent spouse, unless there is a judgment annulling the previous marriage or declaring it void ab initio. The children of the subsequent marriage conceived prior to its termination shall be considered legitimate (Art. 43 (1), Family Code).

6. Children conceived or born of the subsequent marriage under Article 53 shall likewise be legitimate. (Art. 54, Family Code) Under Article 53, either of the former spouses may marry again after compliance with certain requirements, that is, the recording in the appropriate civil registry and registries of property of the judgment of annulment or of absolute nullity of the marriage, the partition and distribution of the properties of the spouses and the delivery of the children's presumptive legitimes.