I have to disagree with the consensus here and say you CAN get too much fiber, because fiber interferes with the absorption of some vitamins and minerals (for example, calcium). Whether he's eating too much I wouldn't say but it IS possible. Also, I wouldn't call "frosted" anything "healthy." It may not be the worst thing in the world but it's not the best, either. Anything processed (you buy it already made) or with a lot of sugar is less than ideal, especially at that age. I'd stick with single ingredient items at first, personally (mashed banana, for example). That's just me, of course, but I wanted to put my 2 cents in because I dont' think it's really "healthy" so if you are thinking you are feeding him something really good for him, I'd say maybe look into that some more. Hope that helps?! Certainly wouldn't hurt to stop giving him the mini wheats and see if the pooping slows down, then you know for sure that's what it is...