There is a point at which every person with human nerves has to say to a child 'Stop that noise.' But suppose the child asks why! There are various answers in use. The simplest: 'Because it irritates me,' may fail; for it may strike the child as being rather amusing to irritate you; also the child, having comparatively no nerves, may be unable to conceive your meaning vividly enough. In any case it may want to make a noise more than to spare your feelings. You may therefore have to explain that the effect of the irritation will be that you will do something unpleasant if the noise continues. The something unpleasant may be only a look of suffering to rouse the child's affectionate sympathy (if it has any), or it may run to forcible expulsion from the room with plenty of unnecessary violence; but the principle is the same: there are no false pretences involved: the child learns in a straightforward way that it does not pay to be inconsiderate. Also, perhaps, that Mamma, who made the child learn the Sermon on the Mount, is not really a Christian."
(From: "A Treatise on Parents and Children")