The risk benefit for children is very clearly in favour of vaccination.
The vaccine was approved in the UK for all children 12-15yo last June, and for 5-11 yo recently IIRC.
Not only has it been approved as safe and efficacious on the basis of clinical trials, many millions of doses have been given worldwide in real world settings, including in that younger age group providing further evidence of safety.
Meanwhile, have either procrastinated on or not proceeded at all with vaccinating these age groups in the UK, we're currently hospitalising record numbers, I think >100\day.
Now that's not, I hasten to add, some kind of health emergency. But as we have the means to stop it, why wouldn't we? Even without with the other concerns around long covid, transmission to older generations, school absences etc.
Surely that is obvious?