Sleep is the natural form of rest observed in all mammals, birds and fish and is an important function that ensures homeostatic balance. These creatures need sleep to perform their daily functions. Sleep cannot be fully described as unconsciousness, and it is a reversible event characterized by a gradual withdrawal from responding to and perceiving the environment. It is an altered state of consciousness from which the person can be easily aroused. It allows the body to rest and the brain to process the information it receives. Sleep is also necessary for memory restructuring and psychological. Sleep is associated with physical growth, emotional-behavioral development and academic performance, especially in children. For a healthy life, children need to get enough and quality sleep. However, sleep problems in childhood seem to be common and affect their sleep quality. The purpose of this book chapter is to examine children's sleep problems and affecting factors.