Allow the children to use their sense of touch to feel around the form and shape of their own head, their eyes, the length of their nose and the outline of their lips. Provide small hand mirrors so that they can look even more closely at themselves, and at the detail of their features. Follow this by discussing how each of the features and indeed the whole head itself could be described simply by an outline shape. Look at the unit 'drawing heads and faces'.
Draw an oval shape upon the board or on a sheet of paper and compare the wide part to the top of a head and the narrower part to the bottom of a chin. Ask the children to sketch their own oval shape making sure that it fills a good part of the paper. Children will benefit from some guidance here. For example, suggest that the oval is at least the size of their outstretched hand. Alternatively, give the children a square shape and ask them to draw the oval big enough so that the square will fit inside.