I've always been a little skeptical when someone says that their child is lactose intolerant, so I say this with a little apprehension, but I'm pretty sure that my 3-year-old is (or it's possible that it is some kind of allergy...). Since the time he started eating solid foods, his diapers have never been what I consider normal. His BM's have always been nasty and grainy. Last year, I finally asked the Dr. about it, and she suggested going two weeks without any dairy and then if his BM's improve, try giving him a big glass of milk and see if they get nasty again.
Two weeks later, his diapers had gotten much better, but when we gave him milk, nothing happened. Some time between then and a few months ago, his diapers got nasty again, so we decided to try again. After the graininess cleared up, he ate a quesadilla and had problems the next morning.
Cheese has been a big part of our diets, so I'm trying to figure out what kinds of snacks can replace cheese sticks. I haven't tried yogurt, but I'm hoping he can still eat that (otherwise I'll have to try making yogurt with soy milk or rice milk). I made salmon patties for dinner last week, and the only vegetable that you can eat with salmon patties is creamed peas and potatoes. The only soy milk we have at home currently is vanilla flavored and I didn't want to eat vanilla flavored creamed peas, so I made two pans of it. A small pan with soy milk (it looked nasty, so I made my Mr. taste it), and a pan with regular milk for the rest of us. My 3-year-old liked it and gobbled it up like it was candy.