Children are having digestive problems?

From what you are saying, it sounds like it could be the milk. Maybe you could just try avoiding milk/cheese for a few weeks until you get the testing done. If the yogurt doesn't seem to bother, then continue with that so they still get some dairy/calcium. I know if I eat too much dairy (namely cheese), I get constipated, too LOL. That is a common intolerance for many people, though. Yogurt may be better tolerated, too because of the probiotics in it.