You can get plain lunch bags and have each child decorate one. Once decorated line them up and have each child drop a valentine item in a bag. You can also take in the capri sun waters for each child as part of the snack. Have fun
Gift ideas, pencils, fruit snack (gummies), no homemade anything, and all food must come pre-packaged.
For a craft, the foam craft stuff seems to be popular amongst young kids. Give each kid a large foam heart, perhaps let them choose between white, pink or red. Then have a bunch of little foam sticky cutouts that they can put on the big heart. I'm sure you can buy sticky cutouts by the bucketful at Michael's or Hobby Lobby or something like that. Let the kids decorate their own heart with the sticky cutouts.
For a game I've seen them do a form of BINGO but use those candy hearts (the ones with the sayings on them) on the BINGO card to block out the square. You can find those candy hearts in the little size or the bigger size. The bigger size is good for this.
if they're exchanging valentines after, or during the party, help them make a cute valentine holder.... my son's last year was pretty simple, it was 2 big hearts made out of construction paper stapled together at the bottom so it held the valentines.