Daddy's little (evil) girl

On my way home today from Brooklyn, there was a couple sitting at the end of the train, 5 feet away from me with their little girl.  She was about 3.  Two stops into the trip, she starts screaming, yelling, and "playing" with her father.  Her mother was across from them reading what seemed like a grocery store coupon sheet.  All of a sudden the little girl runs up to her mother and slaps the coupon sheet with a loud scream.  Then the little girl would hurry up and run back into her father's protective arm and laugh.  This happened for about 3 more times before the mother started trying to discipline her by telling her to stop.  Of course the little girl doesn't stop.  She continues on slapping and screaming at her mom's coupon sheet which was spread out on the mother's lap.  Finally, the mom said to the father, "Tell her to stop!  Tell her!"  He smiles and says NOTHING.  My half of the train is full of older ethnic women whom were ALL STARING at them. They were frowning and shaking their heads b/c if it was their daughter, they'd slap her upside the head by now.  The evil girl is supported by her useless bonehead father.  And together they team-up against mom.  So evil.  

How do children get that way?!?  I would never dare do that to my mother, especially in PUBLIC.  It's the parents fault for not correcting her when wrong.  Are manners not important anymore?!