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Parents are being told not to put face masks on children under the age of three due to a risk of choking or suffocation.
Some outlets are selling face coverings made specifically for babies and toddlers, but Public Health England (PHE) are advising customers not to purchase them.
An update from the agency reads: "We've been made aware that face coverings for babies and very young children are available for sale in England.
"Children under the age of three should not wear face coverings, as they could cause choking or suffocation."
It comes as as new rules on wearing face masks arrive in England today.
Under the regulations, which are enforceable by the police, people now need to wear a face covering in shopping centres, supermarkets, banks, post offices, takeaways and sandwich shops.
Face coverings are also required in railway stations and airports, although some venues are exempt.
It has already been made clear that children under the age of 11 do not have to wear face masks under the new rules.
But Public Health England want to remind parents of the dangers of putting face coverings on very young children.
Professor Viv Bennett, chief nurse at the agency, said: “PHE has been made aware that face coverings for babies and very young children are available for sale in England.
“Guidance is clear that children under the age of three years should not wear face coverings or masks.
"These masks should not be used as they are potentially dangerous and can cause choking and suffocation.
"If you or your child is unwell with the symptoms of Covid-19, then you should get a test and stay at home until you get the result."
There are also exemptions for those who might struggle to wear the mask for medical reasons.
People with breathing problems are not required to wear a covering, which are the same exemptions as for public transport.
Anyone who cannot put on, wear or remove a face covering because of a physical or mental illness or impairment or disability is also exempt.
Despite the rules being enforceable by law, some retail outlets have said they will not challenge customers that refuse to wear masks.
Costa Coffee and Sainsbury’s have both said they will not penalise customers who fail to wear face coverings in their stores.
Supermarket giant Asda said it will "strongly encourage customers to wear a face covering”, but added: “It is the responsibility of the relevant authorities to police and enforce the new rules.”