Source: Emile, or On Education (1762) by Jean-Jacques Rousseau; Book II.

Complete Sentence: Men, be kind to your fellow-men; this is your first duty, kind to every age and station, kind to all that is not foreign to humanity. What wisdom can you find that is greater than kindness? Love childhood, indulge its sports, its pleasures, its delightful instincts. Who has not sometimes regretted that age when laughter was ever on the lips, and when the heart was ever at peace? Why rob these innocents of the joys which pass so quickly, of that precious gift which they cannot abuse? Why fill with bitterness the fleeting days of early childhood, days which will no more return for them than for you? Fathers, can you tell when death will call your children to him? Do not lay up sorrow for yourselves by robbing them of the short span which nature has allotted to them. As soon as they are aware of the joy of life, let them rejoice in it, go that whenever God calls them they may not die without having tasted the joy of life.