It's a relative comparison. Kids are far better at memorizing stuff and dealing with things that have been made "concrete" to them, compared to abstract thinkin

It's a relative comparison. Kids are far better at memorizing stuff and dealing with things that have been made "concrete" to them, compared to abstract thinking - because effective abstraction requires a sort of overall maturity of thinking that very few kids can be expected to develop at an early age! So it's better to just teach the memorization and concrete steps first, and focus on the more abstract stuff later on.