time is finite, time wasted on learning what all the other 4 year olds know is time that can't be spent learning what they actually want to be learning that will make them a unique member of society
any competitive advantage they'll have in the future will come from them knowing something all the other kids don't know, they'll get almost no advantage from learning the same things every other kid had drilled into them as well
(and that's not even accounting for how much more quickly they'll learn what they're naturally curious about)