Be sure they have plenty of space, and that they can get away from the heat source and cool off if they wish. It is surprisingly easy to overheat new chicks, and they can have different temperature preferences. Be sure there is always plenty of fresh water; they shuld never run out, or have their water full of pine shavings or other litter. This can be a little tricky when they are young as they kick up litter so badly. I mush have raised their waterer 3 or 4 times before it was high enough to keep them in fresh water. Lastly, you can add a small amount of molasses to the water. Pasty butt is essentially constipation, which in turn can be related to being overheated and/or dehydrated. I had better luck with Vaseline or Neosporin on their bottoms after I cleaned them, I think because it is solid, it had better staying power -- but oil is OK, too. To clean, it was easiest to me to hold their butts under a slowly running stream of warm water til the stuff soaked off. Took a few minutes, but I didn't have to do any scrubbing or picking.
Good luck!