Hi M.!
I babysit for my cousins daughter and she is about to be 2(yay!) in July. We noticed a change when she would eat diary when she was younger, at first it was constipation, then she would vomit if given too much. Well, one day, we were eating at the table and she was sitting in her high chair, my friend gave her a spoon with some sour cream on it. She , of course had no idea, and we were not certain as of yet, but anyway, When the baby ate it she , of course, got it on her face, around her lips and cheeks. She broke out with a light rash and after trying to figure out why this occured, we remembered that she had that cream all over her face. After that incident the rest fell into place. She can have very small amounts with no affect, but if given too much all those symptoms come back. This was my experience! She has been on lactose free milk and we are very careful! Hope this helps!