Final answer:
My mother asked me to write to my little sister and tell her how much we all miss Amy Kildare and want her to come back home. I explain in the letter that even though I am in high school now, I still remember and miss Amy. I ask my sister to find Amy and bring her back as soon as possible.
Step-by-step explanation:
Dear Little Sister,
I hope this letter finds you well. I recently spoke with Mom and Dad, and they both mentioned how much they miss Amy Kildare and want her to come back home. Mom especially wanted me to write this letter to you and ask you to find her and bring her back as soon as possible.
Even though I was still a little boy when she left, I still remember her and miss her dearly. I am now in High School and play in the school orchestra, but seeing Amy again is more important to me than anything else. If you see her, please tell her to come back right away. Mom wanted me to say thank you for your help.