Put a heart with an animal name (guess you could use states or anything the class is studying) on a heart taped to the children's back. They then have to ask classmates questions and decide what they are. They could then go to the corner of the room with the right classification...mamals, reptiles, etc. Don't know how "Valentines" it is, but it reinforces what they are learning and promotes working together.
What about charades (is that spelled correctly? anyway) or pictionary. Guessing Valentines Day typical fare (candy hearts, val cards) or couples "in love"...Mickey/Minnie, Daisy/Donald, Simba/Nala, Fred/Wilma, Princesses/Princes.
This may cost a little $$. Have cookies or cupcakes and pens that write on frosting to let them make their own sweets with funny sayings. OR even 2...one to keep and one to share