He knows his full name and his birthday and his address, but not his phone number. He knows that he lives in America and that his grandparents live in Ireland, and he might even be able to point out tiny teddybear Ireland on a globe, if you ask nicely.
He knows about the planets and gravity and inertia and evolution and the big bang, and the difference between monkeys and apes, and that Curious George is actually a chimpanzee. He knows many, many A- and B-list superheroes and their associated villians, and some Greek mythology. He knows that many people believe in God, who is kind of like a super-duper-hero, and that his parents aren't sure whether God exists or not, and that he's free to make up his own mind on that one and change it as often as he likes.
I'm not sure what he knows about Santa. I think he knows to keep quiet about it.
He knows that it takes a mother and a father to make a baby (which is more than I knew for a long time) and that people die when they get old or when they get sick and the doctors can't make them better. He plans to make a machine to stop us all dying, when he's grown up. I hope we last that long.
He knows that protein makes him grow and sugar gives him energy but is bad for his teeth and makes him crazy, and that vitamins keep him healthy and that he needs iron in his blood, but he's not too concerned about eating a wide variety of different foods in order to make all that happen.
He knows how to ride a bike and swim (sort of) and kick a ball and climb a tree. He knows how to run after his little sister and stop her with a flying tackle. He knows how to throw a frisbee and fly a kite and how to do up his own seatbelt.
On Wednesday, he spontaneously broke his cookie in half and gave the rest to me.