One of our hosties once had a baby handed to her by a passenger and was told to change her.
She took the infant to the front of the aircraft, where she knew another crew member who was travelling out with her young family on holiday, and duly returned to the offending passenger with a different baby, handing him over with a smile and a simple "there you are"..
I must admit some kids are little sods, but it seems too many parents seem to abdicate responsibility for their kids as soon as they board the aircraft, expecting someone else to ensure they behave.
All mums should have a "scary look" for child control purposes, I don't know if this is passed down through generations or learnt from a manual, but when they have it, it works!
By way of revenge, you could always slip the little dear a couple of cans of full fat Coke as they disembark, should guarantee mummy and daddy won't get much rest for the next few hours!