According to the theory of cognitive development proposed by the psychologist Jean Piaget, the human being goes through certain stages during evolution and growth from birth. He explains that during the Sensorimotor stage that goes approximately from birth to the age of 2, children develop a familiarity with their surroundings through the motor processes, that is to say the ones that are related to the movement, around them using their senses for such perception of the environment.
Therefore in this case, the child would be in the early sensorimotor stage when he has not yet developed completely his abilities to understand the movement of the train and simply loses interest.
