Jessica L. wrote:
>His symptoms are diarrhea, flatulence, swollen stomach (hard as a
rock), abdominal cramping and frequent desire to burp.<

These are not normal symptoms of a milk allergy, but they are 
all symptoms of lactose intolerance. A gastrointestinal bug can 
easily knock out a child's ability to produce lactase, making 
the child temporarily lactose intolerant. That would produce 
symptoms very much like those you list. 

For that matter, in children, unlike adults, vomiting can also be a 
symptom of lactose intolerance, so your daughter may also be 
affected.

I say _may_. Check this out with your pediatrician. You can also 
try eliminating lactose from their diets for a couple of weeks until 
their intestines have a chance to heal.