When I worked in London I had to design stationary and subsequently a website for a local Soho company. They had another company's business card which had this massive eye in it and wanted something similar.
No matter how hard we tried, we just couldn't seem to find the right graphic/photo. They all looked too harsh, cruel or lifeless. It suddenly dawned on us after about three days that our problem was that we were looking at adult eyes when it was a child's eye that gave the more trusting and innocent effect. I think it's more the surrounding area around the eye that does it.
The difference in a close up between an adult and a child's eye was quite subtle on first appearance, however, the subtle difference it seemed to make was quite remarkable!