For me personal this is stupid, this nothing has to do with knowledge or understanding. Do you think a 5 year old kid understand riding a bike? it understand the forward motion, gravity, etc?...I don't think so.
Riding a bike as lot of other stuff require practice, you need to adopt your body and your motor skills and your body need to create the reflex memory.
My English is not that great and i can't find world to explain it better but how every you want to learn to rind your bike it will not make you smarter.
Also kids have lot lot more neurons then adults and that's why they can absorb more information and as they grow the numbers of neurons will drop and its become harder and harder to absorb information as before.
The trick here is to stimulate you kid as young as possible so it can keep as much neurons as it can, which can lead him to be smarter ( easier to absorb information ) when he is all grown up.