Fabric Paint Question

[mercy-mile.livejournal.com]

I looked in the memories and couldn't find anything on this: I've been going crazy with fabric paint and onesies for my son. Now with a lot of the stencils I've done, the paint is kinda thick and makes the area a little stiff, which in some cases is no big deal for me. But I saw something on craftster.org where this girl sectioned off stripes with masking tape and painted the white areas. How would I go about doing this with fabric paint without making it stiff? Can i add a little water to it? Or would that mess with the paint and make it come off in the washer? Oh and if any one has or knows of any kick@$$ stencils for a baby that are either funny or cool, let me know.