Apple of My Eye
Often daughters or sons are referred to as the "apple" of their parent's eye. This phrase originates from King David, who wrote in Psalm 17 to ask God to remember and love David as His child: "Keep me as the apple of Your eye, hide me in the shadow of Your wings." (Ps 17:8).

Emails from site visitors :

Email: This can't be the origin of "apple of my eye" because in the original hebrew it doesn't say that. Literally it is "the little man of my eye." Since it has the same idiomatic meaning, it is translated "apple of my eye" into English. "apple of my eye" doesn't come from Psalms. Sorry.

(来源：英语麦当劳－英语杂志 http://www.EnglishCN.com)