Its the Betty Boop influence via Tezuka Osamu. Following Japanese animators were influenced by him.
http://www.essortment.com/all/animejapanesem_rmpg.htm
Quote: The large, shiny eyes that have become a staple of anime style are actually more a product of history than of culture. In the past, characters in American and European cartoons, such as Betty Boop and Felix the Cat, had disproportionately large eyes. This style was emulated by Tezuka Osamu, one of the most influential founding fathers of anime. Today, this distinctive eye style has become a matter of the animators preference.
I thought of those old paintings of the kids with the big, sad eyes.
Thanks for the info.