It is never too early for a brat to learn that when he/she is waiting in line that he/she may not get what is desired. That is life.
And for the people judging the person who bought 12 pies? He/she could afford the 12 pies and was first in line. He/she could buy everything in the entire place. The fact that these judgemental people are mostly parents is disturbing.
I've bought the last of an item numerous times and only once has some moo had the nerve to try to bargain with me when she realized I had an item in my cart she wanted. Her weak argument on how we could both "win" if I gave up an item in my cart fell on deaf ears. I told her no, we would not both "win" and that it would require me going to another store to find the same item and she would "win" because she conned a stranger out of a in item in her cart. Her escalation to screeching at me didn't change my mind. This is how her children are learning to be assholes with her example.