Do stop the dairy. It really is not good for humans. There are all kinds of issues that dairy can cause. Unfortunately, they are obscure and not readily attributed to dairy. Again, it is actually something that causes health problems in humans. Please visit www.pcrm.org and put diary in the search engine. Also, look at www.strongbones.org and www.notmilk.com. Another great source of info is to read The China Study by T Colin Campbell. Dr. Campbell grew up on a dairy farm and is now a vegan. His research showed that too much animal protein leads to cancer, heart disease, diabetes and immune system disorders. When he was researching a toxin that caused liver cancer in kids, he used a dairy protein to feed both cells in the petrie dish and rats infected with the toxin. The more casein that the cancer was fed, the faster and more agressively the cancer grew. When fed soy protein, the cancer slowed and even stopped, depending on how much soy it was fed. The plant protein even kept the cancer from starting in rats fed a plant based diet.
An optimal diet consists of 90% of calories from plants. Use animal protein sparingly, like a condiment or flavoring for soups and stews. It will take some time to get your son to accept new foods. Dr. Bill Sears, www.askDrSears.com, says it can take 10-14 tries to get a child to try a new food. Be patient. Give him a variety of healthy foods that you want him to choose from. He will accept them in time. And don't worry about calcium. Calcium is actually poorly absorbed from dairy. Yes, it has a lot, but if it's not absorbed, what good is it. There is much more absorbably calcium in dark green leafy veggies, bok choy, kale, and broccoli, as well as sesame seeds. Have you ever tried humus? Kids like to dip veggies. Try giving him 'little' trees (broccoli) to dip in humus, or other salad dressings. Make sure it has healthy oils (nothing hydrogenated) and as few additives as possible. Kids like ranch but most ranch dressing has MSG in it. MSG is an excitotoxin and should be avoided.
I apologize as I have gotten a bit off of the diahrea subject. But I wanted to share background info on dairy so that you can be armed in telling your doc why you no longer drink milk, if you come to the same conclusion that I did. Docs are told by our govt that milk is essential for calcium. But the USDA is an organization that was established to promote agricultural products for farmers. They are not a health organization, they want to sell milk. So, knowing a bit of the history with that, helps to have more info in order to make the best decision for your family. Hope this helps. Be well, D.