Final answer:
Infants are in the sensorimotor stage of Piaget's cognitive development theory, which lasts from birth to around 2 years old. They learn about the world through their senses and motor activities, developing key concepts such as object permanence.
Step-by-step explanation:
Cognitive Development in Infancy
The cognitive development stage that infants are in according to Jean Piaget's theory is the sensorimotor stage. This is the first stage in Piaget's model of cognitive development, spanning from birth to about 2 years of age. During the sensorimotor stage, infants explore the world and learn primarily through their senses and through interacting with their environment via motor behaviors. They engage in activities such as putting objects in their mouths and shaking them to see if they make sounds. A key developmental milestone during this stage is the acquisition of object permanence, which is the understanding that objects continue to exist even when they are out of sight, typically developing between 5 and 8 months old.
While Piaget's theories have been foundational, subsequent research has suggested that infants may have a greater cognitive capacity than he proposed. For example, studies by Baillargeon have shown that infants can have an understanding of the properties of objects much earlier than previously thought. This adds nuance to our understanding of infant cognitive abilities but does not replace the significance of the sensorimotor stage in their cognitive development.