math and mrz, US education varies greatly, not only by state but by city or town (which are the education authorities in the US)
Two of my DGC live in a major city, parents currently researching schools.
The top private schools all offer a stimulating, child-centric play-based for the first two years. Lots of art, music, creativity - as math described above. This is what my own children benefitted from in the UK many moons ago,
Same goes in the upper-middle-class, top-achieving suburbs that surround the inner city.
In contrast, the state schools buckle down to formal academics - phonics, reading, maths, at a tender age. Four-year-olds get worksheets for homework. Similar to the UK nowadays. There's not a lot of difference, to a small child, between Common Core and the National Curriculum.
math, your children were lucky in where you live and the schools they attended.
Interesting how the most privileged children, in schools that annually send respectable numbers of their graduates to Harvard, Yale, and the other Ivies - enjoy this excellent early foundation.
Whereas the predominantly under-privileged kids entering inner-city state schools miss that age-appropriate developmental foundation and buckle straight down to long hours of formal academics.
Sigh.