thanks to everyone who posted their pictures and gave suggestions!
here are our shirts that my 4 y.o.s made (with my help):
i really wanted this to a project that THEY created, so here is what i did to maximize their involvement:
-gave them a bowl of flour and bowl of water...let them spoon flour in and mix to get rid of lumps (this was MESSY, but kept them busy for about 20 mins)
-let them pour their flour/water glue into the squeeze bottles (again, messy, but enjoyable). i found little squeeze bottles at Michael's in the "sand art" section. perfect because the tips were covered, so i was able to snip off the ends to make the openings the size i wanted.
-they practiced with the squeeze bottles, but i actually made the swirls on the shirts (i initially made a template by cutting out a mickey head shape and placing the remaining paper over the tshirt, so i was making my design inside the cutout). i did that with one of the shirts, but then realized that, with some practice on paper towels, it looked more "flowing" if i just did it freehand (and i am HORRIBLE at drawing)
-they will be using the flour water mix to decorate some old hand towels here (this way, they can still make mickey heads without risking the shirts!)
-we let them dry overnight. once they got very dry, i noticed a number of small cracks in the swirls when i was moving them (especially the thin ones)...worth noting because some of the paint leaked in through the cracks
-i let the kids pick out their own colors of tulip fabric paint and they used a small sponge brush to blot on the paint. i put paint tape all around the design just in case they dripped or spattered paint anywhere else on the shirt.
-once dry, i let the kids pick off the flour mix (didn't last long...too tedious!) i wonder if i didn't let the paint dry long enough, as some of the thickest paint came off in small rubbery pieces, pulling along the edges of the swirl when i was chipping it off.
oh, i believe it was this thread where someone asked if you could just put the shirts in the wash to get rid of the flour/water mix? i would say no. i wanted to redo to of the designs prior to paint, so i tried scraping off the wet flour mix, thinking i could then rinse it clean...NOT SO! it was a gooey, pilling mess, so i put it in the dryer then had to scrap all the little flour "pills" off with my fingernails...big pain and the shirts now look a bit worn. i was playing around some more last night and wanted to redo another design, and just scraped the DRIED flour swirl off easily (it comes off much easier than the flour mix with the paint)...so i'd say that this project is perfect for kids to do because you can keep "redoing" the design prior to paint until you get what you want!
hope some of this helps!
Looks like I can do the paint while they are in school. 
I keep going back and forth about doing a second set of the shirts tonight.
