Since I was an art teacher in a private life I know how much fun kids have with tie-dye. I even tie-dyed with 5 fifth grade classes. Let me clarify that, the wonderful art teacher (Dana) that I taught with made the suggestion and I probably looked at her like she had 5 heads. She is the most amazing art teacher I could have worked with an so laid back. It turned out to be a great project and the kids LOVED the outcome. I don't know why it took me so long to finally try it with my girls.
I suggest buying a kit because it contains everything you need. I found it important to use either Procion Dyes or other pigments but not Rit dye. This is a great place to buy all the supplies Dharma Trading Co. or just go to your local craft store and buy one of the kids kits. It will contain 3 dyes in bottles, soda ash, and rubber bands. Soak the fabric in water with Soda Ash. This is important to allow the fabric to really soak up the color. I then let the girls twist in bundle the fabric however they want. When they are ready I twist the rubber band around their little bundles. There are all fancy ways to fold the fabric but for it to really be the girls artwork I let them experiment. I showed them a few twists and then told them to make about 5 that we could rubber band. I then put the t-shirts on a cookie tray and let them squirt away. The bottles work great for kids because the mess can be a little contained. When you are all done with the t-shirts place them in a Ziploc bag for about 24 hours and then wash.
Speaking of crafts... this is an easy self-hardening clay recipe the girls love. I know I have a kiln but the girls sometimes like the instant gratification of sculpting with color clay that will be hard the next day. Warning: Do not leave out around dogs. I found this out the hard way when I thought the dining room was flooding. No it wasn't flooding, it was Hudson and his body reacting to eating so much salt. He still didn't learn and we have to watch him like a hawk when the girls are creating. I can't imagine that it tastes good:)
4 cups flour
1 1/2 Cups salt
1 1/2 cups water
You can either paint it when hard (about 2 days) or we like to add food coloring and then build. Have Fun!