Inner child
As we grow up, we learn to adhere by the norms and rules of the society. There are various things that determine how we group up, how we perceive people around us and how we respond to them. However, no matter how much we group up or how much we are made to adhere or conform to the norms of the society, there exist a self within us, which is untouched and undiluted, which is the seat of instinct and is often only pleasure seeking. This is the inner child of a person.
A concept very similar to that of Id as proposed by Sigmund Freud. Freud theorized that there is a part of the Mind, the unconscious mind or the unconscious that remains hidden at all times, reaching consciousness only through symbolic form in dreams and in some of the behavior people engage in without knowing why they have done so. Freud believed that the unconscious mind is of highest importance in determining factor in human behavior and personality.