Government advisers have recommended that vulnerable five- to 11-year-olds be offered a new paediatric formulation of the COVID vaccine.
The Joint Committee on Vaccination and Immunisation (JCVI) said the vaccination should be given to children at higher risk of COVID-19.
It is estimated that around 330,000 children will fall within this category.
A statement said: "Children aged 5 to 11, who are in a clinical risk group or who are a household contact of someone (of any age) who is immunosuppressed, should be offered a primary course of vaccination."
Further advice regarding the jab for other five to 11-year-olds will be issued in due course after consideration of additional data, and on the Omicron variant more broadly, it said.
The children should be given an age-appropriate dose of 10-microgram doses of the Pfizer-BioNTech COVID-19 vaccine - a third of the adult dose - with an interval of eight weeks between the first and second doses, the statement said.
The JCVI's chair of COVID-19 immunisation, Wei Shen Lim, said: "The majority of children aged five to 11 are at very low risk of serious illness due to COVID-19.
"However, some five to 11-year-olds have underlying health conditions that put them at higher risk, and we advise these children to be vaccinated in the first instance."
NHS Wales will begin identifying eligible children in the new year, the country's health minister has said.
Eluned Morgan added that those under 18 who are eligible for a booster dose will get a booking when they meet the criteria.
The JCVI has also recommended that booster jabs be offered to 16- and 17-year-olds as well as to people aged 12 to 15 who are in a clinical risk group; or who are a household contact of someone who is immunosuppressed; or who are severely immunocompromised and who have had a third primary dose.
The JCVI recommendation came as UK regulators approved the new age-appropriate formulation of the vaccine for use in children aged five to 11.
The Medicines and Healthcare products Regulatory Agency (MHRA) found such a jab to be safe and effective.
A statement by the agency said the approval came after a "robust review of safety data that shows a positive benefit-risk profile for this vaccine to be used in this age group".
The approval was given for the lower-dose formulation that was specifically designed for younger children.
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Dr June Raine, the agency's chief executive, said: "Parents and carers can be reassured that no new vaccine for children would have been approved unless the expected standards of safety, quality and effectiveness have been met.
"We have concluded that the Pfizer/BioNTech COVID-19 vaccine is safe and effective for five to 11-year olds, with no new safety concerns identified. We have carefully considered all the available data and reached the decision that there is robust evidence to support a positive benefit risk for children in this age group.
"Our detailed review of all side-effect reports to date has found that the overwhelming majority relate to mild symptoms, such as a sore arm or a flu-like illness.
"We have in place a comprehensive safety surveillance strategy for monitoring the safety of all UK-approved COVID-19 vaccines and this includes children aged five to 11 years old."
Reacting to the news, Kevin Courtney, joint general secretary of the National Education Union, said: "This is good news for clinically vulnerable primary children and will offer some reassurance to their parents.
"However, it won't impact on transmission rates in schools or make a significant difference to the turbulence that schools and colleges are experiencing due to COVID.
"This makes the case stronger for government to introduce better mitigations."