I wrote a beautiful letter to my parents too. I sneaked it into their bedroom with a gift attached, the night before my wedding, and left it on the dresser for them to find.
It’s a beautiful way to express appreciation.
Some of my friends had a family member/friend put a letter and gift on the table in her parents home, while the family was already by the wedding. The found it when they came home. What a beautiful way to end a simcha!