I copied this from the livestrong.com website.
Milk is a filling beverage, and if your toddler drinks too much of it, he may be less likely to eat more filling foods later. He needs solid, bulky foods in order to pass stool, so avoid letting him fill up on milk, instead. According to Babycenter, he only needs two to three servings of dairy a day. One serving of dairy is 1/2 cup of milk.
Treatment
To help relieve your toddler's constipation, try offering him water or prune juice. Feed him high-fiber foods like plums, prunes, apricots, peas, beans, broccoli and whole grains to get things moving in his digestive system. In addition to milk, cut back on low-fiber foods like cereal, white bread and bananas. Babycenter also recommends that you massage the belly below the navel for three minutes at a time to relieve constipation.
Read more: http://www.livestrong.com/article/327152-can-milk-cause-c...