A council which mistakenly leaked details of thousands of children and their adoptive parents is facing a possible compensation payout of tens of thousands of pounds.
Information about 2,743 individuals was sent to 77 people by Newcastle City Council in an email attachment in June.
At least 35 families are known to be taking legal action.
The authority apologised for the breach, which it said was caused by "human error".
Names, addresses and birthdates of the youngsters were included in a spreadsheet wrongly attached to an invitation to an annual summer party hosted by the authority.
It is understood the council has admitted negligence in relation to at least one claim. The settlement is yet to be finalised.
One of the adoptive parents who is taking legal action told the BBC: "I was angry and astonished because my daughter's new surname, date of birth, the date when she was placed with ourselves, our address and our full names were all disclosed.
"It's the number one concern that adoptive parents have - that their child's information is sent out to the whole world.
"The fear is that the birth family get to know that sensitive information and they come and take her back. It's still in the back of your mind constantly."
Solicitor Andrew Freckleton, of Ben Hoare Bell LLP, said his clients "want to know how the information was disclosed, what the council intends to do to stop it happening again and how it intends to minimise the impact on families affected".
The Information Commissioner's Office is investigating and can levy a fine of up to £500,000.
Newcastle City Council declined to comment on whether it intends to pay compensation to all 2,743 people affected or only to individuals who launch legal action.
A spokesman said: "We apologise again for any distress caused by this human error.
"The Information Commissioner's investigation is continuing and we are co-operating fully."