I have two kids, we have never had this problem. I must have done the impossible.

Surely SOMEone noticed the duct tape?

One thing I learned from having a mom who taught kindergarten and below for over half her life (she progressively taught lower and lower grades as she moved throughout her career, ending up with pre-k) was that there is a difference between kids crying for a reason, and kids crying to be a brat. The first isn't their fault, and the second...well, that isn't really their fault either, as they've learned it gets them somewhere with a parent.

-Mark

We did once, when my daughter was very young she cried for something she wanted in the store. My wife told her she was welcome to stand there and cry but she was going to continue on. Then she kept moving up the aisle. That stilled the tears and my daughter came running up and got in the cart. Never ever had an issue after that. Children are always pushing their boundaries but once you let them know where those boundaries are and which lines cannot be crossed, the problem usually ceases to exist.

Still as other people have mentioned, sometimes kids cry for different reasons. All of us have seen this at one time or another. If it gets too annoying, I just move to a different location. There is absolutely no excuse for anyone to slap someone else's child. I hope they throw the book at the guy.