If you're starting to look for summer time activities to do with kids, you might try tie dying. I had to dye a bunch of shirts for a kids event and because I don't have a dye studio or have dyes of my own I used Tulip dye products bought at the local craft store. The dye and soda ash come already mixed, there is no measusring or mixing and seems pretty safe to use with kids. You just add water and shake.
I prewashed and afterwashed the shirts in synthropol, but the directions don't tell you to do that.
The colors came out a little more pastel than I thought they would, but I like them that way.
I found this big phat marker also by Tulip. It does what it says it should - writes with a big phat line on fabric. If you're into fashion graffiti check it out!
I threw one of these color catcher sheets in the rinse cycle each time I rinsed. I don't know anything about them, or even when/where I got them. But you can see below they did pick up color as they started out being white.
Tulip has made tie dying an easy and fun project to do with kids.