There were a lot of "guess the number of X in a jar" type contests when I was in primary school. I think I won nearly every single one, because I was (one of?) the the only one(s) estimating mathematically. It always seemed pretty obvious to me.
Even with a baseball in the middle (assuming you know there's a baseball in the middle), it's not impossible to estimate, and your guess is still going to be better than someone who didn't try.
That's the thing. You're not supposed to know if there's a baseball in there.
I guess going at it from a mathematical point of view (regardless of tricks) will give you an advantage over a kid guessing something like "a million" or almost any other random number.
Even with a baseball in the middle (assuming you know there's a baseball in the middle), it's not impossible to estimate, and your guess is still going to be better than someone who didn't try.