Final answer:
Piaget's period for birth to 24 months is called the sensorimotor stage, where infants learn through their senses and motor behavior, developing key concepts like object permanence.
Step-by-step explanation:
The period for birth to 24 months in Piaget's theory of cognitive development is known as the sensorimotor stage. During this stage, infants learn about the world primarily through their sensesand motor behavior. A key developmental milestone in this stage is the development of object permanence, which is the understanding that objects continue to exist even when they cannot be seen or heard.