Cut hearts from white paper and write love notes on them with a white crayon. Hide your hearts in strategic morning locations. Place a box of watercolors at the breakfast table, and brush paint over the hearts to reveal the messages.
Make a garden-of-hearts pop-up card with colored paper, markers, and pipe cleaners. Pass the card around the table with dessert on Valentine's Day, and let everyone pick a posy with a special, heartfelt message.