If your child has trouble getting to sleep or has gotten used to waking during the night (e.g., due to a recent toothache or virus, etc.), one great way to help them strengthen their ability to maintain sleep and conquer wakefulness is to say to them: “I’m so glad you’re the kind of person who sleeps through the night because you care about your health. Whenever you find you awaken a little, you just take a deep breath and go right back to sleep. That’s always been the kind of person you are, good at getting yourself back to sleep at night. You have great sleeping skills.”
It is best to say those words (either to your child directly or to others in your child's hearing range) three times daily for at least four days in a row. This technique works because when parents express their positive views (or sadly, negative views as well) about their child's behavior, their child believes them in the moment. Those beliefs about themselves, over time, become integrated as the child's self-image.
For more about the concept that parents' expressed views of their child is one of the largest influences of the child's self-image, please visit my page Positive Eavesdropping.