The British theologian, William Paley, wrote a book called Natural Theology in. 1802. He used history, physiology, and other contemporary knowledge to elaborate the argument for design. He explains that if a person should find a watch in an uninhabited desert, the harmony of its many parts would force him to conclude that it had been created by a skilled watchmaker. It would not have happened by random chance. We would logically know that the watch had not formed from nothing. Thus, how much more intricate and perfect in design is the human eye, with its transparent lens, its retina placed at the precise distance for forming a distinct image, and its large nerve transmitting signals to the brain.
A ladder is made for climbing, a knife for cutting, and a watch for telling time; their functional design leads to the conclusion that they have been fashioned by a carpenter, a smith, or a watchmaker. How easy it is to conclude that the obvious functional design of animals and plants is the work of a Creator.
Gather the children around and watch this wonderful video that teaches design: http://www.kids4truth.com/watchmaker/watch.html