Does a Muslim woman, a foreigner, incur sin by marrying a Muslim man without a contract for 15 years and bearing 4 children, then having a contract drawn up in court, followed by the husband's absence for 11 years, and what is the status of the children, and is a new marriage contract necessary upon the husband's return?

A legally valid marriage (Nikah (definition)) is one that fulfills the necessary conditions. The marriage contract for a Muslim or Christian woman is handled by her guardian (wali) from her own religious community. If no such guardian exists, the Muslim judge (qadi) or Islamic centers will arrange her marriage. Documentation in court is not a condition for the validity of the Nikah. If any of the conditions for Nikah are not met, or if there was no contract to begin with, then the marriage is void. There is no sin upon one who was unaware of the religious ruling. As for the children, they are attributed to their father if the spouses believed the marriage to be valid; otherwise, they are attributed to the mother. There is no need for a new contract if it has been renewed in court.