This single thought, once fully understood by a mother, will save her a great deal of trouble in answering the incessant questions of her children.

The only essential thing in many cases is to _say something_ in reply to the question, no matter whether what you say communicates any information or not.
If a child asks, for instance, what makes the stars shine so, and his mother answers, "Because they are so bright," he will be very likely to be as well satisfied as if she attempted to give a philosophical explanation of the phenomenon.

So, if he asks what makes him see himself in the looking-glass, she may answer, "You see an _image_ of yourself there.

They call it an image.

Hold up a book and see if you can see an image of that in the glass too." He is pleased and satisfied.