In virtually all cases, the decision is up to the adoptive parents regarding how to inform the child that he or she has been adopted, and at what age to do so, if at all. Although a non-profit adoption agency (if one is used) might mail newsletters and solicit funds from the parents, traditionally, it has been extremely rare for them to communicate directly with the child (usually, adoption agencies do not contain the word "adoption" in their name).
But closed adoptions meant that birth parents were left wondering if the child they placed for adoption had grown up healthy and happy with a loving family. They meant that adoptees had no medical history to rely on, nor any answers about the circumstances leading to their adoption. This lack of information made it difficult for birth parents and adoptive families to contact one another if they wanted to meet later on in life, and it made it more difficult for adoptees to form a positive self-identity.
In all adoption searches, it is uncommon to find both the birth mother and father at the same time. A separate search, if desired, can be done afterwards for the father. Since males seldom change their surnames, and the mother might have additional information, it is usually easier than the initial search for the birth mother. In many cases, adoptees are able to do this second search for their birth father by themselves (or they try before paying for assistance).