If under the age of 18 and their line of work does not fall under front-line i.e. not eligible in the JCVI list, the green book (page 18) provides further information on vaccinating in children and risks. In summary:

“Children and young people have a very low risk of COVID-19, severe disease or death due to SARS-CoV-2 compared to adults and so COVID-19 vaccines are not routinely recommended for children and young people under 16 years of age…. Given the very high risk of exposure to infection and outbreaks in institutional settings, vaccination may be considered for children with severe neuro-disabilities who tend to get recurrent respiratory tract infections and who frequently spend time in specialised residential care settings for children with complex need“

The clinical decision to administer the vaccine to healthy under 18’s would need to be made by a prescriber under a PSD.