The stage of cognitive development, according to Piaget, in which child displays 'object permanence' is

Sensori Motor is the first stage of Piaget's theory of cognitive development. It extends from birth to approximately 2 years. The main development during this stage is the understanding that objects exist and events occur in the world independently of one's own actions (object permanence). Object permanence means knowing that an object still exists, even if it is hidden. It requires the ability to form a menal representation (i.e. a schema) of the object.