married woman cAN get a baby with another man if husband doesnt get kids as per mahabharatha

If anybody is issueless, he can adopt the son of his daughter (douhitra) with the permission of his son in law and daughter. Such adopted son shall have all rights over the property as a natural son. 

If any married couple has no issues, the wife, with the permission of her husband, may have sexual intercourse with another virtuous man and beget children. Such children are called Kshetraja and they are also regarded as the natural sons of that married couple. The husband shall treat them as his own sons.

If any man begets children through another married woman, other than his wife, he is called Goodhaja. Those children are regarded as the natural sons of her original husband.

http://www.telugubhakti.com/telugupages/monthly/mahabharat/content1302.htm

kids son

If an unmarried girl gives birth to a child, such child is called Kaaneena. After her marriage, that child is considered to be the legitimate son of her legally wedded husband.