Young children often play fantasy or pretend games. It's especially common between about 2 and 7 years or age. It starts in simple ways. The Swiss psychologist, Jean Piaget described how as early as 15 months his daughter Jacqueline lay down on a cloth, sucked her thumb and blinked her eyes. Piaget thought she was pretending to go to sleep, and indeed Jacqueline laughed at the same time indicating that she was not being serious. The next day her mother's coat collar became the 'pillow', and two weeks later the tail of her rubber donkey! When a bit older, a child might put a doll or teddy to 'sleep' in a similar way. By 3 or 4 years, quite complicated socio-dramatic play sequences can take place, in which several children act out complementary roles such as mother, father and baby; monsters and Dr. Who; doctors, nurses and patients; or activities such as shopping, or putting out a fire. Some children have imaginary companions with whom they talk and carryon activities. In all these examples, the actions of the child have some pretend or fantasy component; and indeed the children are generally quite aware of this distinction between fantasy and reality.