I wouldn't switch foods just yet - a rushed food switch will just make their tummies worse, plus california natural is actually one of the easiest foods on the digestive system because it doesnt have too many ingredients.
I would start with the pumpkin for now, or white rice (zoey loves the white rice - because it's hot she thinks its a treat). They also might have just gotten into something they shouldn't have eaten, so it might go away easily.
I do have one question though - do they have loose stools all the time or just certain times of the day.
And as a side note, the "resolve spot magic" is a great cleaner the get rid of stains from booty blowouts