Other people knowing about personal information about the adoptee’s birth family, reasons for being adopted etc. before the adoptee knows can lead to problems. Problems can arise especially with your other children knowing details before an adoptee knows these details.
You can say something to Aunt Martha casually about your adopted daughter's birth family being involved in drugs or that the adoptee’s birth mother could not care for another baby. Then Aunt Martha mentions this to another family member and before you know it everyone in your family has heard and details have been added along the way. One day your adopted daughter is playing with other children at a family function and lo and behold a cousin starts talking about your daughter’s adoption details. I understand it started innocently, but in the end the adoptee is the one hurt and betrayed.
You do not think it has happened think again. I have known other adoptees that this has happened to. One adoptee I know was told by her old sister (not adopted) that her birth father was Hispanic and made him sound like some mafia dude. She had olive complected skin but did not really appear to be Hispanic. The adoptive parents did not know who the birth father was or what he may have looked like. This adoptee went to search for her birth father and was quite surprised he had blonde hair and fair skin.
Another adoptee learned she had siblings when she was given up for adoption in this same family type of a way. Learning information this way for an adoptee can be traumatic and be very painful.
Any information about an adoptee's adoption, past or birth family should come from the adoptive parents. To insure this will happen and protect the adoptee, do not share details unless the adoptee already knows of them.
Related post:
Protecting Adoptees Past Information