For this backdrop, you will need:
Plastic tablecloths from the dollar store ( I used four, but it you want to photograph taller children, you might want to grab more)
green crepe paper
Take a long piece of twine and tape it to a smooth surface that is a couple of inches taller than the height of who you want to photograph. You will need to tape it on the two ends and then in the middle as the table cloths will weigh the twine down.
Since everyone I was photographing was 4-years-old and under, I folded the tablecloths in half and draped them over the twine. If you want the backdrop to be taller, just wrap the top edge of the tablecloth over the twine and tape the tablecloth to itself.