I overheard a conversation my 5 year old son was having with another kid while waiting in line to get into preschool class. They were arguing about how many seconds it would take to do something (I forget what). The other kid says it will take 4 minutes. My son replies immediately, "No way, that would be 240 seconds!"

My brother who's a 6th grade math teacher came to visit this weekend and likes to quiz him. He asked him what -12 + 9 is and he answered correctly. I had no idea he even knew about negative numbers. He then went on to teach him exponents.