Over here we have two types of adoption, open and closed. Open is just that, the parent(s) are on the adoption records were they can be called on later in life if needed.
Closed adoptions, well. It takes sometimes an act of god to open them. In these cases most of the time it's through an agency where the birth parents leave the children there, then they are adopted out. Depending on the state even a court order can't crack it. Some agencies barcode parents.