A more thorough explanation:

The presumption of legitimacy is a legal concept in family law that assumes a child born to a married couple is the legitimate child of the husband. This means that the husband is presumed to be the father of the child unless proven otherwise.

There are three situations where the presumption of legitimacy applies:

• The child was conceived or born while the parents were married, even if the marriage was later found to be invalid.
• The parents got married after the child was born, and the father agreed to have his name on the birth certificate or to support the child.
• The father welcomed the child into his home and treated the child as his own.

For example, if John and Jane are married and have a child, the law presumes that John is the father of the child. However, if Jane has an affair and the child is not John's biological child, John can challenge paternity and prove that he is not the father.

The presumption of legitimacy is important because it provides legal protection for children born to married couples. It ensures that they have a legal father who is responsible for their care and support.