My most perfect decadant adult Valentine's gifti is a heart-shaped bon bon called a parchita that is filled with liquid passionfruit flavored caramel.
I was going to describe it but I would border on x-rated. While I love caramel, I don't usually like passionfruit ... yet I could live on these chocolates. It is sold by Chuao
As to kids ... not decadant, but fun ... there is an ad occaisonaly on the site for personalized valentine message pink & white M&M's. There was some sort of deal too, IIRC.