A child can be sealed to both sets of parents.
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Thank you for posting your question about child sealings. Yes a child can be sealed to both biological and adoptive parents. Read the policy below:
Children born to a man and a woman who have been previously sealed are considered sealed to their parents (born in the covenant).
Children who are not born to previously sealed parents may be sealed to their parents. Sealings may be performed by proxy on behalf of deceased children.
A deceased child is usually sealed to birth or adoptive parents. Where justification exists, deceased children may also be sealed to stepparents, foster parents, or grandparents. A deceased child can also be sealed to a couple who intended to adopt the child but could not complete the adoption before the death of the child
Children are not sealed to **** couples, even if the couples have been legally married. Children of **** parents may be sealed to biological parents or grandparents.
If all persons involved are deceased, no special approval is needed. If any of the parties is still alive, please see your priesthood leader.