If they have not been previously infected then they are offered a single dose.
“Why not vaccinate 12-15-year-olds who have had COVID-19 disease?
Since recovery also provides protection against new infection, vaccines are not currently offered to 12- to 15-year-olds who have had COVID-19 disease. This corresponds to the recommendation for 16 years and upwards, where those who have undergone COVID-19 disease are recommended 1 dose of vaccine instead of 2 doses.”
www.fhi.no/en/id/vaccines/coronavirus-immunisation-programme/coronavirus-vaccine/#vaccination-of-children-and-adolescents
They also only offer a single dose to previously infected 16-17 year olds.