[Your Address] [City]
Date: [Date]
Dear Grandma and Grandpa,
Thank you so much for the wonderful [gift, e.g. wristwatch] you sent for my birthday! I opened your parcel first, and it was the best gift of the whole day. Everyone at the party admired it.
It fits me perfectly, and I have decided that I will wear it for every examination as my lucky charm. Even more than the gift, your letter with all its blessings made Mother's eyes moist and my heart very happy.
I miss you both and our evening walks. My holidays begin on [date], and I am already counting the days until I visit and eat Grandma's [favourite dish] again.
Please take good care of your health. I promise to write again soon.
With lots of love and respect, Your loving grandchild, [Your Name]