Khan Academy Kids is incredible. Watching a toddler battle brain fatigue learning the number two because they want to is terrible and terrifying. If you let them pace themselves and treat it as a game without forcing a schedule they easily get two years ahead of schedule. But it is so much an outlier.
No. wouldn’t. And the kids themselves wean themselves off the kids version at about age 6 suddenly by whatever interests them - seems all:zero for all the kids I’m aware of using the kids version. But the greatest impact in my opinion is understanding a structured lesson is a skill they mastered before formal schooling which puts them ahead. Not to mention early use of english - not our mother tongue.