"Sharenting" - where parents share personal information about their children on social media - is the "weakest link" in risking online fraud and identity theft, warns Barclays.
The bank says parents are compromising their children's future financial security with so much online sharing.
Barclays forecasts by 2030 it could cost almost £670m in online fraud.
The bank's security specialists say social media means identity fraud has "never been easier".
Barclays is warning that parents might be "lulled into a false sense of security" and fail to realise they are making their children "fraud targets" in the future, by publishing so much personal information which will remain online.
Identity fraud
Parents are being told that information on social media is vulnerable to being misused to hack passwords or for identity fraud scams.
The bank says parents can reveal names, ages and dates of births from birthday messages, home addresses, place of birth, mother's maiden name, schools, the names of pets, sports teams they support and photographs.
Barclays warns that such details, which will still be available when young people are adults, could be used for fraudulent loans or credit card transactions or online shopping scams.