Do you have to adopt a child already living with you if you aren't the parent?

I'm writing a story and this is a question I need an answer to. If the birth parent allows their child to live with another adult, but nothing is legalized, is it still necessary? And if so, what is the process?Do you have to adopt a child already living with you if you aren't the parent?
A parent can allow their child to stay with anyone they want, with permission. However, if the caretaker wanted to be able to do things like authorize medical care for the child or enroll the child in school, they would need to seek to become the child's official legal guardians-- not necessarily adopt.





Laws vary by area on procedure for this stuff. The first step would be contacting a family law attorney, but what happens after depends on the rules in the state/country where the story is set.Do you have to adopt a child already living with you if you aren't the parent?
if the child is not adopted, then the child will still belong to the birth parents, so the other adult can't act on behalf of the child unless the parent authorize the other adult to become a legal guardian.