Lincoln's new "friend"

This school year Lincoln has a new school "friend". This is a picture of Lincoln and Abby at her birthday party at Excite this past weekend.
Lincoln tells me and Ron things like... "Abby is soooo adorable...", "Abby is my girlfriend" and that he is going to marry Abby one day.... So, we hear a lot about Abby now... She is in his preschool class, his Sunday church class, and his Little Crowns choir. She's a super sweet girl, but what's with having a "girlfriend" at age almost 5???