What's the middle number from zero to infinity?

Ah Pa was reading to Cayen a book on dinosaurs. Midway, he paused as Cayen looked very troubled , as if he's going to cry. Ah Pa asked him on what's wrong and encouraged him to share his problem so perhaps they could work it out together. This is what happened next.

C: Ah Pa, what is the middle number from zero to infinity ?

P: Erm , since infinity is never ending , and for whatever number you name, there will always be a next bigger number , there's no such value . Or perhaps the middle number is "infinity divided by 2"

P: actually Cayen, so far we have been teaching you 1,2,3,4,5... 10 but we never taught you about negative numbers. Actually the smallest number is not zero , it can be negative 1,2,3,4....10 and it can even be negative infinity. 

C: oh, so zero is not the smallest number. I thought zero is the smallest number. 

Just as Ah Pa was going on with more examples about positive numbers and negative numbers, suddenly Cayen exclaimed , " I know! The middle number of infinity and negative infinity is zero!" 

What a revelation ! Ah Pa was shocked too. He hadn't thought about it that way . And he certainly wasn't expecting it from a 4.5 year old boy. 

With that,  Ah Pa encouraged him to continue to think and ask questions whenever he has doubts. And because it's already so late, Ah Pa asked him to quickly sleep because tomorrow is Thursday and soon it would be Friday. 

Cayen made his last statement of the day , " And Thursday is the middle Number in the week" . Whoa , he's really into all things middle right now .