My children loved to be read to when they were little as most children do. I read a lot of the classic fairy tales as well as told some from memory and often made up stories. When my second child, was around three years old I was reading him a story and he stopped me and said, "Mama, you forgot to say One a pona time." It was so cute and funny I never forgot it. I made a point, after that, even if I was reading a story that didn't start out "Once upon a time", to add it in just for him.
I read that phrase for years without really thinking about the meaning but recently I was writing a story and thought about using that in the beginning. I did some research and the phrase "Once upon a time" simply means "There once was". These stories always end in "and they lived happily everafter". I love the old classic stories and apparently so do many people for they are redone and expanded upon over and over again. Just recently I visited a Barnes and Noble and there are novels based on the story of "Alice in Wonderland", "Cinderella" and "Peter Pan". These stories have stood the test of time and have been with us for generations.
So if you have trouble writing a story, read a classic fairy tale and see if there isn't a new story there waiting to be told. Maybe tell the story of Cinderella from the mice or Fairy God Mother's point of view. You don't have to write children's books to do this. Write an adult love story or tragedy based on one of these ideas and they don't necessarily have to end in "happily everafter" unless you want them to. Look at the book "Wicked" and "Confessions of an Ugly Stepsister" by Gregory Maguire. He took classic children's fairy tales, twisted the story and turned them into adult novels.
There are ideas everywhere; we simply have to look for them. ;0)