Ann,

I would be concerned about a child who was vomiting at 4 days of age and
becoming dehydrated.  The differential diagnosis is wide and includes some
serious conditions that need assessment by a physician.  These include:

1)  Infection, particularly urinary tract (rare)
2)  Gastroesophageal reflux (common)
3)  Congenital abnormality of the GI tract (rare)
4)  Pyloric stenosis (rare at this age)

I suspect that the vomiting is unrelated to the breastmilk unless mom is on
some unusual medication.  There may be no serious problem here but is
suggest the child see a physician soon.

Khalid

Khalid Aziz
Memorial University of Newfoundland