Final answer:
Object permanence is the concept that objects still exist when not seen, usually developing by 8 months.
Step-by-step explanation:
Object permanence is the understanding that objects continue to exist even when they cannot be perceived. This concept is a key component of Jean Piaget's theory of cognitive development. Piaget proposed that object permanence typically develops in stages during infancy.
Typically, this cognitive development occurs by around 8 months of age during the sensorimotor stage, according to Jean Piaget's theory. Cognitive milestones like this are essential in a child's development as they lay the foundation for further cognitive capabilities, such as problem-solving and understanding the persistence of objects.