I used the colors Red, Yellow & Blue with prints in spots & stripes. Kinda loud, I know, but perfect for kids! It adds some visual punch to an otherwise pretty drab room.
I simply measured the chair backs and made a little pillowcase to slip over the back. The letters & numbers were cut using my Cricut, which cut down on my hand cutting time dramatically. I had been told that Cricut's could cut fabric, but I had never tried. It took a little adjusting, but if finally worked and saved me time cutting each piece individually.
I used the Cricut cartridge "Storybook" as well as no sew interfacing. This made it so I could just iron on the letters & numbers without having to applique each one individually. I'm thinking of making a matching bunting next.
*Cricut Tip* Iron on your "no sew" interfacing to a piece of fabric the same sizes as your cutting mat (either 6X12 or 12X12). Make sure your cutting mat is nice and sticky (new). Place your fabric/interfacing piece paper side down to the cutting mat. Set your needle pressure to "max" and speed to "med" or "fast". Adjust as needed.