When four-year-old Deirdre wants an item or an activity, she will attack her parents with her fists until they laughingly and protestingly give her what she wants. Her parents' decision to give into Deidra's demands in this fashion

Encourage the behaviour and make her believe that this is the way to manage what she wants.

Explanation:

Right now Deirdre is very young now so her tantrums are manageable and her parents are in a better physical position to handle it. As she gets older she will understand that whenever she wants something she must use aggression and she must defy her parents in order to get it.

As she moves into her school years this behaviour will be continued with the individuals that will tolerate it.

Later she will also learn that there are persons where she can continue this behaviour and persons that do not tolerate it. She will act accordingly.

will reinforce her behavior and possibly create a long-lasting pattern of aggression and defiance.

Explanation:

As long as Deirdre parents continue to give her what she wants after attacking them with her fist, they are simply reinforcing the bad behavior and as time goes on, this reinforcement in a negative behavior can create a long-lasting pattern of defiance and aggression which would see Deirdre use such aggression anytime she wants something because instead of stopping the negative behavior, her parent continued to reinforce it.