Nottingham Primary Care Trust (NPCT) has admitted that "several laptops" have been stolen, one of which contains information on about 11,000 young children.
The computer contained the names, addresses and dates of birth of children from the Newark, Mansfield and Ashfield areas, and was one of three stolen from an office at King's Mill Hospital in Sutton-in-Ashfield following a burglary last week.
The information on the laptop is password protected, according to NPCT.
"We would like to reassure the public that this matter is being fully investigated and we are taking every step to prevent this happening again," said NPCT chief executive Wendy Saviour.
"We are very sorry for any difficulties that this may cause and greatly regret that this theft has happened."
The trust has written to all families affected by the theft and has set up a helpline.
"Organisations such as King's Mill Hospital must have security procedures and policies in place to ensure that data is safe in the event of laptop theft, particularly when personal information is involved," said Donal Casey, a security consultant at IT consultancy Morse.
"Although it is excellent news that the laptop is password-protected this does not make it entirely safe.
"Where employees need to carry sensitive data of this nature, IT managers should be looking at more complex security measures, such as encryption, biometrics and ensuring that employees are educated on security policies and procedures to ensure such data is not put at risk."
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