Jake: What’s 100 plus zero?
Me: 100.
Jake: What’s 1,000,000 plus zero?
Me: 1,000,000
Jake: What’s infinity plus zero?
Me: Infinity.
Jake: What’s infinity plus infinity?
Me: Infinity.
Jake: Is infinity the nothing number too?
Me: :eek::D:cool:
*I don’t know what the name is for the set of counting numbers plus aleph null, so I just called them the naturals in the title, since aleph null is the most “natural”-y infinite ordinal anyway. What is the name for this set? Is there one?
These are sometimes called the “co-natural numbers”, but it’s not a terribly popular term.
Amusing anecdote, but what happened next after you answered that last question of Jake’s? [Also, how old is Jake?]
He turned four in March. I forget exactly what I said to him in response on that occasion but it would have involved explaining again what infinity is (my gloss for the kid is “a number bigger than all the numbers you use to count with”) and explaining that if you add any more to that, it’s still bigger than any number you use to count with so it’s still infinity. His response was simply “oh” which can mean “I see” or “this is over my head and let’s talk about something else”. There have been no further math conversations since then which might have shown which “oh” this was. 
I am pretty sure its the latter–but I also think he’ll get it fairly soon if the same point comes up a few more times in the future.
I’m nearly 40, and relatively bright, but I have always had trouble grasping the concept of infinity.