A Norwood social worker left a detailed report about four children at the side of a house in London in December after attempting to deliver them to the children’s prospective adoptive parents.
The documents, which contained details of the neglect and abuse suffered by the children and details of their birth families, were taken before the occupants of the house returned home half an hour later and have never been recovered.
The charity reported the incident to the ICO, which investigated and discovered that the social worker had not been trained in data protection, which exacerbated the seriousness of the case.
The ICO said the children were all aged six or younger and that sensitive information about them could be in the hands of strangers.
"The fact that the social worker had received no training on how to look after extremely sensitive information is truly staggering," said Stephen Eckersley, head of enforcement at the ICO. "This breach was entirely avoidable."
He said the seriousness of the breach left the ICO with no choice but to impose a fine. "We hope that this breach acts as a warning to all charities that they must fulfil their legal requirements under the Data Protection Act by handling people’s information correctly," he said.
The ICO said the fine would be reduced by 20 per cent to £56,000 if it was paid by 12 November.
A Norwood spokeswoman said: "Norwood took immediate steps to tighten its procedures to ensure that an incident of this kind will not be repeated."
The ICO warned in August that charities were liable for fines of up to £500,000 for offences relating to their storage of sensitive information and offered them free advisory visits.