Simply replace the unfilled areas such as "" and "[date]" with your information.
I will really miss you when you are gone. I know you are working and that is very important. We are all sad when you are away but we will be very happy when you come home.
While you are gone, please call me and say goodnight to me. [Parent staying home] will keep me safe and tuck me in, but I want to tell you I love you before I go to sleep. I can't wait to tell you all about my [day/something exciting in child's life]. When you come home, we will play [favorite game] and go to [favorite location]. Be careful, look both ways when crossing the street, and brush your teeth.
I love you [Mommy/Daddy],