: of, relating to, or being the stage of cognitive development according to Jean Piaget's theory in which thought is egocentric and intuitive and not yet logical or capable of performing mental tasks
Piaget believed that during the preschool period and up to about age 6 or 7, children are in a preoperational stage—too young to perform mental operations. David G. Myers
The preoperational child will invariably point to the taller, thinner glass. He believes that it contains more water because the water level is higher. Dorothy G. Singer & Tracey A. Revenson