When DH met me and took up my raw milk habit, he had a mild digestive upset for the first couple of days. This is known to happen for some people, as raw milk -- like natural yogurt, and other living foods -- does affect your gut flora. It's a change for the better, but the process can sometimes be a little unpleasant at first. So it's best to start slowly, especially if you're the sort of person who tends to have a sensitive stomach (e.g., has to avoid the tap water when traveling, even in developed countries with proper sanitation), or if you've been eating a typical American diet with lots of sugar and refined foods.
Other than that, there have been no problems for any of us. I've been drinking raw milk for years; I'm on my fourth pregnancy drinking it, and all three of our children drink it. The children get far fewer colds and "tummy bugs" than their friends do, and have never been sick to their stomachs for more than a few hours. By the time I get around to finding the Pedialyte, they're all better, ready to eat and drink normally again, and back to running laps around the house.
ETA: We drink certified raw milk. If it weren't so stringently inspected, I'd definitely want to visit the farm and check things out for myself, especially before feeding it to little ones.