It is easy enough to have a Valentine's card making kit for kids. Mine is made from die cut hearts from recycled cardboard and colored card stock, toilet paper tubes that have been painted, cut, and folded to look like hearts, and chenille stems. Then I provide the blank cards, envelopes, some other papers that they can cut and glue, glue sticks, scissors, and markers.
Here are some cards that some sweet girls made for me from this kit.
Here is the card that my youngest son made for my husband for Valentine's Day.
Also using supplies from the kit, this girl made this origami heart for her mom.