The World Health Organization says children aged 12 and over should wear masks to help tackle the pandemic.
Masks should be worn when 1-metre distancing cannot be guaranteed and there is widespread transmission, it advised.
It is the first time the WHO has issued guidance on masks for children and comes less than two weeks before pupils in England return to school.
Although a small number of schools have said they will require children to wear masks, including James Gillespie’s high school in Edinburgh and Eaton Mill primary school in Milton Keynes,the government says that masks are “not recommended” for primary or secondary school children.
WHO stressed more data was needed to better understand the role of children and adolescents in the transmission of the virus.
Its guidance says ages six to 11 should wear masks on a risk-based approach. Factors such as transmission rates, the child’s ability to use the mask and adequate adult supervision should all be taken into account.
Children aged five years and under should not be required to wear masks based on the safety and overall interest of the child.
The WHO first advised adults to wear masks in public in June, and the government made them compulsory in shops in England from 24 July.
Gavin Williamson, the UK’s education secretary, said earlier this month that research by Public Health England indicated there was little risk of the virus being transmitted at school, but the agency subsequently stated that secondary school pupils are just as likely to transmit the virus as adults.