Dave actually it depends how you frame a group most at risk.
The significance or the R number rises with the number of infected in the community. That is to say an R number of 2 in a population where 10,000 are infected is less of a threat to the whole population than if 10 million are infected.
The old and vulnerable are more at risk of serious illness and death from the disease than children and young people.
However it was realised very early on that children and young people were the greatest spreaders of the disease, numerous studies have confirmed this to be the case.
So the sensible option was to isolate the children and young until a vaccine was available and administered to that group first to control the infected population.
What the government did though was keep children and the young in school when they were restricting the adult population. Then the government went the precisely most hazardous route, they separated the kids into two groups and key workers children were permitted into schools but the other were not and restrictions were placed on them.
The key worker kids were able to mix and spread the virus, that was then taken home to the parents many of them working as health workers or nursing home staff with obvious results.
The super spreaders should have been targeted for restrictions and vaccine first rather than the vulnerable because many of those are near the end of life anyway and are in a minority.
The government failed to manage the risk to the whole population by focusing on protecting the vulnerable. Many of the vulnerable will tell you that they would rather be able to hold their loved ones and children / grandchildren than be protected by oppressive measures which severely reduces the quality of their remaining life, those measures are also shortening the remaining time for many.
The government’s strategies and policies have encouraged the virus, quite benign to many, to rip through the entire population eventually infecting the old and vulnerable.