The inner process of creating requires two things: asking and receiving.
People often fail to get in a receiving mode because of its paradoxical nature. To receive what you want, you must be free not to have it. The longer you're willing to wait, the sooner it will come.
If your child is complaining about not having what s/he wants right now, s/he's stuck in the asking mode. Ironically, parents often exacerbate the problem by saying or thinking essentially the same thing: "I want the complaining to stop NOW!"
To help your child get in a receiving mode, model it: get in your own receiving mode about your child's receiving mode! :) How? Simply imagine your child happily anticipating the fulfillment of his or her desire.
As you deliberately enjoy that vision (even if your child is still complaining), you become the change you wish to see.
And when you demonstrate the receiving mode often, your child will eventually fall into it with you — naturally and willingly.