It is proposed here that there is a sensitive period in the first two to three years of life during which humans acquire a basic knowledge of what foods are safe to eat. In support of this, it is shown that willingness to eat a wide variety of foods is greatest between the ages of one and two years, and then declines to low levels by age four. These data also show that children who are introduced to solids unusually late have a narrower diet breadth throughout childhood, perhaps because the duration of the sensitive period has been shortened. By reducing the costs associated with learning, a sensitive period for food learning should be adaptive for any omnivore (including early humans) that remains in the same environment throughout its life.