Sorry to be rude glorygloryeze but you clearly don't have a good grasp of the maths.
Assuming* each subset of kids is roughly the same in terms of fitness, age, health, gender etc.
Either scenario could happen, depending on how deadly the disease is and how efficacious the vaccine is.
In scenario 1: Vaccinated deaths = 450/9500 = 4.7% death rate and unvaccinated deaths = 50/500 = 10% death rate, so vaccination clearly works and more than halves your risk of death.
In scenario 2: Vaccinated deaths = 50/9500 = 0.5% death rate and unvaccinated deaths = 450/500 = 90% death rate, so vaccination is incredibly powerful as almost everyone without it died, yet with it only 0.5% died!
You don't seem to grasp that if 99.9999% of people are vaxxed, then almost everyone in hospital would be vaxxed.
*This is another fatal flaw in your reasoning. Nearly all the decrepit old giffers have been vaxxed, so of course the people dying from the disease (i.e. decrepit old giffers) have been vaxxed... that does not mean the vax doesn't work. Surely you can see that?