What is 'adopt as care dependent'?

I use that option all time, a parent can't use it because they are already caregiver but when there is multiple children in the house then they can care for each other or I have one family and they needed help with the garden and the household so I brought in a non family member and she used this option on the twins so she can help with the parenting of the twins. Teens can also adopt younger siblings or toddlers in the household so they can help too. It gives the non parent more ways to help raise the child and then they can help with teaching them parenting stuff and they can ground the children too. this option just lets non parents have more say in the kids life that live with them. And more than one sim can adopt as caregiver. And it doesn't take away from the actual parents.