Angelina Jolie's daughter Shiloh has a new imaginary friend

According to reports, Angelina Jolie's daughter Shiloh has a new imaginary friend, where she name her as Amy.

A source tells celebrity blogger Perez Hilton, "Shiloh says she likes Amy more than Knox and Viv" and at dinner time Shiloh will refuse dinner, claiming that "Amy's not hungry."

I don't seem to understand when some children have imaginary friend because I never had one. Are these children having a bit of mental problem when they are having such friend? Will their parents start to worry about this problem?

Source