Final answer:
The first stage in Piaget's theory of cognitive development is the sensorimotor stage, where infants acquire information about the world through their senses and motor skills. They develop object permanence, the understanding that even if something is out of sight, it still exists.
Step-by-step explanation:
The first stage in Piaget's theory of cognitive development is the sensorimotor stage, which lasts from birth to about 2 years old. During this stage, infants acquire information about the world through their senses and motor skills. They learn about objects by exploring them with their senses, such as putting objects in their mouths to see if they are edible or shaking objects to see if they make sounds. Through this exploration, young children develop object permanence, which is the understanding that even if something is out of sight, it still exists.