When we were little, my mother would not let us play or use the gift until we wrote out thank you notes. My husband and I wrote our thank you notes for our wedding while we were on our honeymoon. Many people commented to my parents they had their thank you notes before we got home. My mother said my husband was the only son-in-law that ever sent them thank-yous for gifts and actually wrote to them about once a year. (We live in CA and they lived in WA State.) So we passed on the importance of writing the notes to our daughters, and they even write us notes.
My mom finally told my sisters if she didn't get a thank you note from their kids she would stop sending them gifts. They sent one note.