We live in a volatile society and as such, many lawyers are faced with clients that admit to us that they fathered a child with a married man or woman. Then, they wonder, "Who's the father?" Under California Law ( CA Family Code Section 7540), there is a conclusive presumption of paternity for children that are born to a married woman. To be more specific:
1) The mother must be in a valid marriage,
2) The mother lives with the husband,
3) The husband is not sterile
4) The husband is not impotent
If all these factors are present, then the child is presumed by law to be the child of the mother's husband. In a case in which the father is an entirely different person than the husband, the presumption is rebuttable through a motion for a blood test that must be filed within two years of the child's birth (CA Family Code Section 7541).
As people said in the old days, beyond the law the only person who knows the father of a child is the mother. Thus, if you have any doubts that your significant other's child is not yours, consider filing a motion for a blood test within two years of the child's birth.