In ancient India, 12 different kinds of offspring were regarded as the father's legitimate heirs. They don't all have to be their legal father's biological offspring.
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12 Types of Children (Legal Heir) in Ancient India
Aurasa : biological son through a woman in a typical marriage, with the Y chromosome belonging to the father.
Putrikaputra : When there isn't a son, the female is treated as one, and her son inherits the estate legally (ex : Babruvahana, born to Arjuna and Chitrangada, but became legal heir of his maternal-grandfather.)
Kshetraja : although husband is not the biological father, wife's womb. (For instance, Kunti and Madri give birth to Pandavas.) The children may be born even after the husband passes away, and they will still be considered the deceased father's heir.
Dattaka : legal adoption or vedic ritual adoption.
Kritima : A youngster is fed and raised as a son, but there are no formal adoption procedures followed. The child grows up and views you as their parent