Sharon Davies, of education charity Young Enterprise, warned children as young as six were increasingly being targeted by scammers.
She said: “The financial pressures of the pandemic and an increase in social media usage have left young people more vulnerable than ever to online scams.
“Younger victims are being targeted through online gaming, where scammers encourage them to hand over card details to buy currency or characters for the game at a reduced price.
“While older children are also vulnerable through social media and tempted by the likes of cryptocurrency, which can lead to big losses.”
Ms Davies said more education was needed in schools and at home to protect children from criminals who preyed on their vulnerability.
More than half of children aged between the ages of three and 15 spend hours each week playing games online, according to telecoms regulator Ofcom, which are flooded with scammers posing as other players or tech support.
Despite the risk, a quarter of parents do not have any security measures in place to protect their children while online, according to recent research by Lloyds Bank. More than half gave their children access to their own finances.
Mel Stride, chairman of the Treasury committee, said he was aware of “heart-breaking” scam cases and called for more action to shield children and teenagers from criminals online.
Amber Burridge of Cifas, Britain’s biggest independent anti-fraud agency, said children were especially at risk of identity theft because of the amount of personal information they shared online, such as birthdays, names and addresses.
She added: “We have seen an increase in children falling victim to scams, where they are socially engineered to hand over their own or parent’s card details.
“It will only get worse amid the cost of living crisis as children don’t want to ask their parents for money and will be more vulnerable to offers of a cheap deal or extra cash. Online safety should not be a taboo subject within families.”