Sometimes holding their lower bellies in some warm water, even having the faucet run right onto the area, and gently massaging the area at the same time will help get them to go, and when you finish with the water, whether it helps them or not, you could put a dab of baby oil, mineral oil, or even vegetable oil in the anus, and use a q-tip to get a dab INSIDE, (but not too far, so you don't hurt them) can make it easier for them to go if they are constipated. Also, add some light karo syrup to their feedings, as that is supposed to help prevent constipation.