There were a couple years that my children made small heart picture frames, using fun foam. We just cut out a small rectangle for the picture and decorated a heart-shaped frame. Another cute craft was to use tiny puzzle pieces and we created a broche/pin. I think they were spray-painted in advance so the red color was translucent and the puzzle colors made it look like various shades of red. The pieces were glued together into a heart shape (we xeroxed heart shapes and they used that as a guide to make a heart and used glue dots to glue each piece onto another) Then you buy adhesive pin backs at Michael's and attach them to the back.
Games to play: Find the paper hearts - hide many, many, paper hearts around the room and put a sticker on four or five of the hearts. One award goes to the person who has the most paper hearts and other awards go to who has found a sticker heart (one prize per person). Also, a cute game is "the charm game" Attach a tiny heart charm on a a piece of yarn or thin string (something that a charm easily slide on). This string should be large enough to accommodate at least 10 children in a circle - or larger depending on the size of your playgroup. The string has to be knotted at one side and the charm has to be able to slide over the knot easily. One child is picked as the "center person". The "center child" closes their eyes. The music starts, the children-in-the-round have to hold the string with both hands (all hands in the same direction) and pass the charm on the string, when the music stops, the child who has the charm must conceal the charm in their hands and ALL of the children have to pretend THEY are holding the charm too. The center child picks the person, they think, is holding the charm - the charm holder gets a small token prize if they "fool" the person. If the "center person" picks correctly, they get the small token (or....because they are preschoolers - EVERYONE gets a prize!) You can determine what is fair as far as who should go in the middle and when.
Have fun!