Dr Marinho calculated the excess of deaths by unspecified acute respiratory syndrome during the pandemic, and found that there were 10 times more deaths by unexplained respiratory syndrome than in previous years. By adding these numbers, she estimates that the virus in fact killed 2,060 children under nine years old, including 1,302 babies
Unfortunately we don't have the data to hand to do a similar look, but for the last year, under 24 year old deaths from all causes are well down, there has been an increase since feb, but this is pretty much opposite to the over 85's increase.
I think it's reasonable to assume that over 85 excess deaths strongly correlates to covid prevalence, so if under 24 year olds were dying due to covid then we'd see excess deaths in the young age groups at the same time - perhaps slightly adjusted due to different timing of infection (likely they'd be before you'd assume?)
Whereas the ONS excess deaths stats show no such correlation, excess deaths in the under 24 age group has been consistently negative almost all the time until mid feb, and particularly low in the weeks before Christmas at the peak of school outbreaks - app.powerbi.com/view?r=eyJrIjoiYmUwNmFhMjYtNGZhYS00NDk2LWFlMTAtOTg0OGNhNmFiNGM0IiwidCI6ImVlNGUxNDk5LTRhMzUtNGIyZS1hZDQ3LTVmM2NmOWRlODY2NiIsImMiOjh9
So I think we can say that there's no appreciable hidden deaths from covid in the UK in children. So if the impact is real, it's either something about Brazilian variants or something about the conditions which have caused it (such as lack of care of other respiratory diseases due to stressed healthcare etc.)