Four studies were done to test the hypothesis that, although knowledgeable about some important facts concerning visual perception, 3‐year‐olds have not yet learned that lines of sight must always be straight. Subjects of 3 to 5 years of age were asked whether they (Study 1) or toy observers (Studies 2–4) would be able to see objects via looking paths that were curved rather than straight: for example, by looking through a bow‐shaped hollow tube or along the curve of its outside wall. Consistent with the hypothesis, 3‐year‐olds gave no evidence of possessing this straight‐line‐of‐sight rule. In contrast, 5‐year‐olds showed at lea