Now available in the amazon & etsy shops are blank heart magnets! This is the same 4x3.5 inch heart shape available as a printed magnet, just with blank white paper.
Could be a fun coloring project for the kids. Or, maybe you could have a magnetic board and have guests write their names/message on a heart magnet.
Also available are 8 packs of circular color book magnets:
Flowers, a couple of animals, a butterfly- just cute things for the kids to color. Order multiple packs for a classroom activity!