Statistics for the US, where childhood is a bit more dangerous than the UK (thanks, lack of gun control!), show that childhood deaths in the 10-19 age range happen at an annual prevalence of approximately 30 per 100,000. For reference, pediatric cancers kill about 2-3 children per 100,000 per year in this age group. Motor vehicle accidents account for about 10-15 per 100,000 depending on the specifics of where the child lives.
According to the best estimates we have from WHO about the mortality rate of this virus in all age groups, children 10-19 are .2%, or two-tenths of a percent, 2 in 1000, likely to die from coronavirus infection.
To get an equivalent per 100,000 ratio from our number in 1000, we multiply the numerator and denominator by 100, and that's 200 in 100,000.
If every person in the UK contracted the virus (obviously an unlikely scenario!), 200 out of every 100,000 children 10-19 years old again, according to WHO figures, and we've seen none lower than those anywhere would be expected to die.
However, we don't think that's really the ratio who will contract it! Let's in fact say that containment measures and social distancing are somewhat effective, enough to confine infection to about 20% of the population.
20% of 200 is still 40 out of every 100,000. This is a higher rate than combined "all causes" mortality for this age group, by a significant amount.
Even if we've significantly underestimated the number of "mild" cases of coronavirus in children let's say 10 times more children have undiagnosed cases that are so mild they're never tested, compared to children who are confirmed positive we'd be looking at reducing that again by dividing by 10, for a result of 4 children in every 100,000.
So even if there's a huge population of "dark cases" where children get immunity without illness, and even if population spread is contained, we can expect coronavirus to kill more 10-19 year olds this year than pediatric cancer.
If we are NOT vastly overestimating the death numbers for children, we are looking, even in a relatively well-contained scenario, at a number of deaths far exceeding "all causes mortality" for their age group in a typical year.
I cannot understand when people look at a .2% death rate for children and shrug it off. Absolutely nothing in the world we have seen in our lifetimes with a potential to infect so many people kills off .2% of children. Parents absolutely dread pediatric cancers, but even highly-optimistic analysis of the statistics generated so far would indicate that this is a greater danger to the 10-19 year olds of 2020 than cancer.