When do children start to retain memories?
Childhood amnesia
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Some research has demonstrated that children can remember events from the age of one, but that these memories may decline as children get older.[3][4][5] 
Most psychologists differ in defining the offset of childhood amnesia. Some define it as the age from which a first memory can be retrieved. This is usually at the age of three or four, but it can range from two to eight years.[6][7][8]