Never quite understood why it was deemed necessary, but my security guard trainer thought it was essential for our training.
It really burns your nose, mouth and eyes. The eyes hurt the worst and can burn for up to an hour. (If any of your wives carry that stuff or mace tell them to aim for the eyes if attacked) One of the things that will ease the pain faster than water is Johnson's Baby Shampoo.
Very sorry your innocent little four year old had to go through that pain.
I also understand it's a tough situation for mail people.