Artcle 89, Chapter 3 of the Civil Code of the Philippines

Art. 89. Children conceived or born of marriages which are void from the beginning shall have the same status, rights and obligations as acknowledged natural children, and are called natural children by legal fiction.

Children conceived of voidable marriages before the decree of annulment shall be considered as legitimate; and children conceived thereafter shall have the same status, rights and obligations as acknowledged natural children, and are also called natural children by legal fiction. 


Explanations:

A legal fiction is a fact assumed or created by courts which is then used in order to apply a legal rule which was not necessarily designed to be used in that way. For example, the rules of the United Kingdom Houses of Parliament specify that a Member of Parliament cannot resign from office, but since the law also states that a Member of Parliament who is appointed to a paid office of the Crown must either step down or stand for re-election, the effect of a resignation can be accomplished by appointment to such an office. The second rule is used to circumvent the first rule.

Legal fictions may be counter intuitive in the sense that one might not normally view a certain fact or idea as established in the course of everyday life, but they are preserved to advance public policy and preserve the rights of certain individuals and institutions. A common example of a legal fiction is a corporation, which is regarded in many jurisdictions as a 'person' that has many of the same legal rights and responsibilities as a natural person.
Legal fictions are mostly encountered under common law systems.

The term "legal fiction" is not usually used in a pejorative way, and has been likened to scaffolding around a building under construction.
In the phraseology of the English or American law, natural children are children born out of wedlock, or bastards, and are distinguished from legitimate children; but in the language of the civil law, natural are distinguished from adoptive children, that is, they are the children of the parents spoken of, by natural procreation.
In Louisiana, illegitimate children who have been acknowledged by their father, are called natural children; and those whose fathers are unknown are contra distinguished by the appellation of bastards. The acknowledgment of an illegitimate child shall be made by a declaration executed before a notary public, in the presenee of two witnesses, whenever it shall not have been made in the registering of the birth or baptism of such child. Such acknowledgment shall not be made in favor of the children produced by an incestuous or adulterous connexion. 

Fathers and mothers owe alimony to their natural children, when they are in need. In some cases natural children are entitled to the legal succession, of their natural fathers or mothers.
Natural children owe alimony to their father or mother, if they are in need, and if they themselves have the means of providing it. The father is of right the tutor of his natural children acknowledged by him; the mother is of right the tutrix of her natural child not acknowledged by the father. The natural child, acknowledged by both, has for tutor, first the father; in default of him, the mother.