Thank you EVERYONE for the information. I know the basics of dyeing and I would NEVER let the girls around the dyes not only are they toxic this is going to be done at MY HOUSE and I don't want a mess I will NEVER get out!
I was also thinking something like muslin didn't know if it needed to be bleached or unbleached, so thank you.
I will check around for fabric dyes and see what I can come up with. If I don't find much I will just order and start a new hobby, lol dyeing fabric!
I love the idea of letting them "draw" a picture on the pillow cases and then letting them dye them.
Thanks again everyone! you all are great! :)