A stepparent adoption creates a legal relationship between a stepparent and stepchild that previously did not exist. It declares that the person being adopted (stepchild) is legally the child of the adoptive parent (stepfather or stepmother), and the child becomes the adopting parent’s legal heir.
The stepchild becomes entitled to all of the rights and privileges and subject to all of the obligations as if they were a child born to the adoptive stepparent.
A stepparent adoption only ends the rights of one of the birth parents. The spouse of the stepparent retains their rights as a biological parent of the child.
The Nuts and Bolts of California Stepparent Adoption