Knowsley Council is investigating how papers containing sensitive information about two looked-after children were sent to the wrong person.
The Merseyside authority has apologised to the family involved about the “extremely regrettable incident”, which it blamed on an administrative error and a breach of procedures.
The children’s services department sent the confidential papers last Wednesday.
A council spokesperson said today: “The individual who received these papers in error contacted the council and we made immediate arrangements to secure the information. We are very grateful to the individual for acting so promptly.
“An inquiry is under way to determine exactly how the error was made. Action will be taken and additional safeguards put in place to ensure this does not happen again.”