I am nothing if not well stocked with fabric scraps, so the kids went to town picking fabrics to cut into heart shapes. I tried not to interfere with their choices. The more naive, the better with these cards.
I had them cut out hearts freehand, some with pinking sheers and some with standard scissors.
Both of my kids like to use the sewing machine. There is nothing special to sewing on the paper and any crookedness makes them better, I think.
I'm not a scrapbookin' type, but I recently got this set of vintage-style alphabet rubber stamps from Etsy. Lots of supply shops carry them, but set your search to "shop local" (ie. USA) if you don't want to deal with overseas shipping. They are perfect for finishing off the cards and, well, scrapbooking too ;)
Happy Valentine's Day!