KMR Stage 2 formula

I started the kittens on this a few days ago because they are 4 wks old and it is much cheaper. The one kitten has runny stools everywhere. She insists on getting into corners and exploding but does pee in the litter tray Is it to rich? Should I go back to the regular or is goats milk easier on her stomach? She is eating some wet food out of a dish but really likes her bottle.