The senses are our window to the world. They enable us to perceive the abundant world around us. We then piece these experiences together to form our image of the world. Experiences that involve several senses at once are particularly memorable. As they develop, children are constantly faced with new cognitive challenges. Babies learn primarily by observing and imitating. They try out the same things again and again. Around the age of three, children start to perceive the difference between themselves and the world around them; this is a stage of rapid cognitive development.