Pierce is a two-year-old boy who loves his "lellow-lee" (yellow blanket) and won't take a nap without it. pierce's yellow blanket would be considered a (n) :

I believe the answer is: transitional object.

Transitional object in this context refers to the type of object that somehow provide the owner with a certain level of psychological comfort. Other examples would be a professional fighter who refuse to fight in competition before kissing the pendant that belong to his parents at home.