The counting has not been consistent over time. It's been maybe 6 months out of a pandemic now in its third year that this has been measured.
Saturation is very high due to increased transmissibility, and often unknown due to decreased severity. Seropositivity in blood samples show at least 75% of kids have been exposed already, probably higher in the Northeast where I am since the latest minisurge has hit us already from the 12 subvariant.