There's one more factor/advantage that should be accounted for: children and their parents/grandparents engage in a natural feedback loop. Parents try and teach

There's one more factor/advantage that should be accounted for: children and their parents/grandparents engage in a natural feedback loop. Parents try and teach the children words, once the child starts repeating the words the parents get excited and repeat it back, and so on and so forth. It's like having extremely dedicated, enthusiastic tutors for those five years.