put some paint in a bowl, add a bit of water and stir. you don't want it complete liquid, but the consistency of a thin gravy ... if that makes sense. then you pour a bit onto the paper in blobs and let the kids blow it with a straw.
not so much a pretty picture, but it's more for the interaction, to see the cause and effect. Sam likes to be in control as much as possible - all 3 1/2 year olds do, right? so this was entertaining and fun for him to do.
we used construction paper, but the directions had said to use non-absorbent paper. probably something more like butcher paper ... which I need to go buy some of that stuff, it's good for so many things.
any straw will do - I stole some from the last place we had fast food for dinner. :) but you probably could use the crazy, swirly ones too ... although it might take more effort to blow enough air through to move the paint.
experiment and let me know what you come up with. enjoy!