I am too wimpy to embark on activities involving glitter, glue, and four children by myself these days, so I enlisted the help of my good friend and lifesaver, Bev.
If you want to make your own singing heart valentines, just cut up a few cereal boxes and some sheet music, then water down some glue and decopage the music to the cardboard. Decorate with hearts of whatever materials you have on hand. We used cut-outs from felt and construction paper, and some cute wooden heart beads that I found at an epic yard sale last summer. Glam it up with glitter or other sparklies (I think I preferred the plain style, but our audience was 4, 3, and 2 year old girls, so glitter was required). Write "You make my heart sing", or "You put a song in my heart", or whatever other cheesy sentimental musical phrase you can come up with on them. The writing will stand out more if you use a colored gel pen, but I didn't have one :).
The girls actually did turn out some pretty cute ones (and Bev and I managed to make a few without toddler assistance), but aesthetics tend to fly out the window when you break out the glitter. This age group does not understand the "less is more" concept. Just remember:
lots of glitter = lots of love.