In your analogy, swimmers may have gone down 90% but kids are still being submerged in water as much as ever if not more. The vast majority of traffic deaths are people INSIDE cars.
[0] https://www.construction-physics.com/p/why-are-so-many-pedes...
"Deaths of children under 10 are actually down significantly (167 deaths in 2009 to 98 deaths in 2023), and deaths for ages 10-19 are down as well."
Kids playing on neighborhood streets show continued improvement... In fact IIHS pedestrian fatality data says that 1-13 year olds are the group with the HIGHEST reduction