[randomdata]

That makes sense, but suggests that calculus is perhaps the most difficult concept to wrap one's head around, which flies in the face of the idea that is easy to teach to children. It is not clear where the breakdown occurs here.

[dougabug]

Calculus is not easy to teach to children. We fail to teach it adequately to most college students in their first two years of study. Even a few historically noteworthy mathematicians failed their first contact with the subject.

Elementary linear algebra is far easier to understand and motivate. We can deal with finite, concrete examples without having to delve into the subtle complexities of limits, continuity, and infinity.

[randomdata]

But it was said that "since kids can easily understand it" and it is not clear how that resolves.

[dougabug]

That statement was clearly false. With an amazing teacher, an extremely bright student, focus, patience, time, etc., sure we can have the next Galois… but in the vast majority of cases, we should avoid setting kids up for failure by expecting them to easily grasp things which took humanities greatest minds centuries to grasp. Newton “invented” Calculus in the 17th Century, but these ideas had been percolating since Archimedes and even before going back two millennia.