Common decency in this case being giving three year olds anything they ask for.
It is common decency for adults to give baseballs to kids.
Again, the kid's reaction was irrelevant.
These people are asshats because they thought it was more important to keep a baseball for themselves than it was to give it to a kid.
Why is a random ball handed from a stranger important to the kid?
Going back to the argument that catching the ball is more thrilling than the ball itself, how thrilling is it, even when you are 7, to be handed a ball that someone else caught? And when you are 3, you really have no clue about the value of a baseball tossed into the crowd. You know someone just got something and you didn't, so it is time to cry. Nobody involved in this situation would give 2 [expletive] about that ball in 24 hours, including and especially the 3 year old.