If your child is whining for something you'd rather not give, you might notice a knot in your stomach. That means you're NOT centered. ("Knot-centered"?:)
Anything you say or do while you're off center is likely to make things worse. Better to get centered first. Take a deep breath and tell yourself...
"I will take no action until I feel centered."
You may find that no other action is needed, because children want centered parents more than the things they whine for.