Interestingly, children as young as 5 show an aptitude for understanding overarching concepts of calculus.[1]

This makes sense: it is much easier to talk about "rates of change" and "accumulation" in simple terms and show how they are related using models that appeal to children. We don't need to dive right in to the notation and algebraic manipulations to get across the basic idea. That can come later when children can handle the rigor. For now, let them play with it. That makes math a lot more fun and less draining, esoteric, impenetrable.

[1] https://www.theatlantic.com/education/archive/2014/03/5-year...