Infants as young as 15 months can understand false beliefs about an object's location, and 14.5-month-olds can understand false perceptions, while 18-month-olds can understand false beliefs about an object's identity. These findings challenge the traditional view that false-belief understanding emerges around age 4. Spontaneous-response tasks, such as violation-of-expectation (VOE) and anticipatory-looking (AL) tasks, suggest that infants can attribute false beliefs to others much earlier than previously thought. In VOE tasks, infants look longer when agents act in ways inconsistent with their false beliefs. In AL tasks, infants anticipate where an agent with a false belief will search for an object. These tasks reveal that infants can understand false beliefs about location, identity, and perception. However, elicited-response tasks, which ask children direct questions about an agent's false belief, are difficult for young children. These tasks require multiple cognitive processes: representing the false belief, selecting a response based on that belief, and inhibiting responses based on their own knowledge. Young children often fail these tasks because these processes are not yet fully developed. The response account suggests that toddlers can succeed in indirect-elicited-response tasks where they infer an agent's goals without directly answering questions about the agent's false belief. The evidence indicates that infants have a psychological-reasoning system with two subsystems: Subsystem-1 (SS1) handles basic mental states, while Subsystem-2 (SS2) handles more complex states like false beliefs. SS2 becomes operational by the second year of life. Alternative interpretations of the findings include associations, unusual events, ignorance, and behavioral rules. However, the response account is supported by evidence from neuroscience, showing that brain regions involved in false-belief reasoning develop later in childhood. Ongoing research explores whether infants and toddlers from different cultures consistently succeed in spontaneous-response tasks, whether autistic toddlers have difficulties, and whether other spontaneous-response tasks can be developed to take advantage of toddlers' richer linguistic and behavioral abilities. The response account is being tested through various experiments, including VOE tasks where toddlers observe an adult's false belief. The findings suggest that infants and toddlers can understand false beliefs and use this understanding to infer others' goals and intentions.Infants as young as 15 months can understand false beliefs about an object's location, and 14.5-month-olds can understand false perceptions, while 18-month-olds can understand false beliefs about an object's identity. These findings challenge the traditional view that false-belief understanding emerges around age 4. Spontaneous-response tasks, such as violation-of-expectation (VOE) and anticipatory-looking (AL) tasks, suggest that infants can attribute false beliefs to others much earlier than previously thought. In VOE tasks, infants look longer when agents act in ways inconsistent with their false beliefs. In AL tasks, infants anticipate where an agent with a false belief will search for an object. These tasks reveal that infants can understand false beliefs about location, identity, and perception. However, elicited-response tasks, which ask children direct questions about an agent's false belief, are difficult for young children. These tasks require multiple cognitive processes: representing the false belief, selecting a response based on that belief, and inhibiting responses based on their own knowledge. Young children often fail these tasks because these processes are not yet fully developed. The response account suggests that toddlers can succeed in indirect-elicited-response tasks where they infer an agent's goals without directly answering questions about the agent's false belief. The evidence indicates that infants have a psychological-reasoning system with two subsystems: Subsystem-1 (SS1) handles basic mental states, while Subsystem-2 (SS2) handles more complex states like false beliefs. SS2 becomes operational by the second year of life. Alternative interpretations of the findings include associations, unusual events, ignorance, and behavioral rules. However, the response account is supported by evidence from neuroscience, showing that brain regions involved in false-belief reasoning develop later in childhood. Ongoing research explores whether infants and toddlers from different cultures consistently succeed in spontaneous-response tasks, whether autistic toddlers have difficulties, and whether other spontaneous-response tasks can be developed to take advantage of toddlers' richer linguistic and behavioral abilities. The response account is being tested through various experiments, including VOE tasks where toddlers observe an adult's false belief. The findings suggest that infants and toddlers can understand false beliefs and use this understanding to infer others' goals and intentions.