But they must be travelling with a fully vaccinated parent or guardian, say tourism authorities.
Under-18s travelling to mainland Portugal with a fully vaccinated parent or guardian will not have to quarantine, authorities have confirmed.
The statement follows two days of confusion over whether Portugal’s new rules applied to minors.
Under the rules, adults must quarantine for 14 days unless they can prove they received their second vaccine dose a fortnight before arrival.
But children aged 12 and over do have to show a negative Covid-19 test.
This must either be an RT-PCR test taken 72 hours before their departure, or a lateral flow test taken 48 hours before their departure.
These rules are specific to mainland Portugal, which is currently on the amber list, meaning those travelling back to the UK from there must quarantine for 10 days at home.
Different rules apply for travellers to Madeira, which will be added to the UK’s green watch list from Wednesday.
The new rules have already had an impact.
“It was carnage and chaos for every business in the Algarve,” says Joe Mountain who runs Sandy Blue Villas, renting accommodation in the Algarve.
“Yesterday we were contacted by 50% of UK guests with forward bookings for this summer.
“People were in meltdown and just not understanding the rules. It’s impossible to find answers.
“For us, it has been continued uncertainty for the last two months, with a real lack of ability to plan. We rely on that and it is critical that we get UK guests this summer.”
In another development, Malta’s health ministry has said travellers arriving there from the UK from Wednesday will need an official NHS letter to prove their vaccination status.
“Only the paper version of the NHS Covid letter will be accepted, which can be requested online or by calling 119,” the health ministry said.
“The vaccination certificate will be not accepted in digital or downloaded PDF form. It must be the printed version issued directly from the NHS.”
Malta has said only “fully vaccinated travellers” will be allowed to enter the country from the UK – and this includes children aged 12-plus. Children under 12 will be permitted if they are accompanied by parents or guardians who have had both doses.
The Maltese government has said those aged between five and 11 must also show evidence of a negative PCR test taken within the previous 72 hours before arrival.
The measures have been introduced for UK travellers, in particular for those not fully vaccinated, amid fears they could spread the Delta variant of coronavirus, which was first identified in India.