I will use Italy as i know that the best.
The government has published 1 in 500 as a case fatality rate for under 10s. Case fatality is not the same as infection fatality, it is only confirmed cases. To work out the infection fatality rate out you need to know how many people really had the virus, and serological studies in the worst hit part of Italy estimate the number of people who have had the virus is around 5% of the population.
There are around 280,000 under 10s in this area, so you can estimate 14,000 have had the virus, and 3 have died. Call it a 1 in 5,000 infection fatality rate, but remember that is only an estimate, and this is the worst area in the country. Nobody knows how many under 10s really die from the virus. But it is definitely not 1 in 5 million.
@stevoc - In both Spain and Italy it's the under 2 age group that is most affected of all children. I'm not aware of any deaths closer to age 10. Whilst it is a form of breathing issue, asthma is not one of the main identified comorbidities for the virus.