A nursery has told parents and staff they will need to use a fingerprint scanner to gain access to the building.
They must press their finger on to an electronic pad every time they arrive at one of two private nurseries in Kent.
The door will only open if they are on the biometric database.
Critics have condemned the use of such technology in a nursery. They warned that children will grow up thinking it is normal to provide a fingerprint to get into a building - without appreciating the dangers of a surveillance society.
Campaigners claim the systems will encourage staff to rely on fallible technology instead of memorising parents' faces - potentially leaving children less safe, particularly if the scanner breaks down.
Bosses at Springfield Lodge Day Nurseries, who look after 279 children at two sites in Swanscombe and Dartford in Kent, defended the system, which went live yesterday.
They claimed it would improve security while helping staff monitor the number of children and carers in the building at any one time.
Each child's family can register up to three guardians whose fingerprints will be scanned and loaded on to the database.
No prints will be taken from children themselves and parents can still make emergency pick-up arrangements with friends or relatives using a password system.
The nursery's managing director, Linda Berriman, said: 'The parents have been really pleased with it because they have seen this additional security put in place at no extra cost. We had one or two parents with reservations in the first instance. One of the biggest concerns was the collection of information because of recent reports about loss of data by organisations.
'But there is no additional storing of information as a result of this system being introduced.
The children themselves aren't even aware.
'All they see is Mum and Dad dropping them off and touching a pad before the door opens.' She acknowledged the problem of 'tailgating' - where one person holds the door open for another following behind - and admitted the nursery would rely on the goodwill of parents and staff to prevent security lapses.
But campaigners predicted problems with the fingerprint scanning system - which they warned was likely to spread 'like wildfire' to other nurseries.
Simon Davies of Privacy International said: 'There comes a point where technology does not provide the answer. The history of biometrics shows that people are seduced by such technology - they soon become reliant on it and then stop using their common sense.
'Will staff stop bothering to memorise people's faces? What happens when the system suddenly breaks down? 'Just as importantly, children will grow up thinking it's fine to give fingerprints for any reason.' The row comes at a time of growing fears over the safe storage of personal data following a string of security breaches.
Last year, HM Revenue and Customs lost computer discs carrying the personal and bank details of all 25million families who were claiming child benefit.
A recent report by Britain's data protection watchdog, the Information Commissioner, warned that such lapses are taking place at a rate of one every working day, with a third blamed on private sector operators.