The Office of Fair Trading has given online game producers until 1 April to comply with guidelines relating to in-app purchases, or else face legal action.
The online games industry has been criticised for the ease at which it is possible for children to make in-app purchases, sometimes leading to bills of hundreds of pounds for parents.
Gaming apps that are often free to download make money by charging users for items like in-game currency and other special features.
A survey undertaken last year by Microsoft revealed that over a quarter of parents had reported unauthorised payments to game developers, costing them approximately £31 million each month.
Earlier this month Apple agreed to refund at least $32.5 million (£19.8 million) to customers over unauthorised in-app purchases, following a complaint from the Federal Trade Commission.
In order to avoid purchases made by children without their parents' consent, Apple has updated its App Store and Google has amended its app policies.
However, the OFT is demanding that more is done by game producers to protect consumers against hidden costs.
"In-game payments are not authorised and should not be taken unless the payment account holder, such as a parent, has given his or her express, informed consent," the new guidelines state.
The OFT has also offered advice to parents on how best to avoid unwanted in-app purchases.
"Many children enjoy playing these types of games," said Clive Maxwell, chief executive of the OFT. "This rapidly growing creative sector has also brought wider economic benefits.
"Our principles make clear the type of practices that games makers and platform operators should avoid. Parents and carers have an important role to help protect their child and their bank balance."