Kiddushin, Chapter Four, Mishnah Ten
This mishnah and tomorrows mishnah deal with establishing the identity of the wife of a man and children who come from overseas. In order to marry them to other Jews, he would need to establish their identities.
1) If a man went overseas together with his wife, and then he, his wife, and his children returned, and he said, Behold, this is she [who went with me overseas,] and these are her children, he need not bring proof with regard to the woman or the children.
2) [If he declares,] She died [abroad] and these are her children, he must bring proof with regard to the children, but not with regard to the woman.
Section one: The mishnah rules that if the man went overseas with his wife and now returns with children he need not bring proof of the lineage of any of them. He need not bring proof of his wifes lineage because he already checked it when he married her. He need not bring proof of the childrens lineage because it can be assumed that they are the children of his wife. The Talmud adds that the children must be hanging on her, meaning acting as if they are his children. [Ill add that every time I return with my family from overseas, our children are certainly hanging all over us.] If the children are not treating her as their mother, we might suspect that they are not her children.
Section two: If the woman with whom he went abroad died there and then he returns with children, claiming they are her children, he must bring proof that this is so. However, once he does so, he need not prove the fitness of the woman, because he already did so when they were married. It seems that he would need to have witnesses who would testify that these are his (deceased) wifes children.