Can constipation cause a baby to vomit?

Rarely. Constipation can be accompanied by abdominal pain in infants; those prone to reflux may get upset and vomit due to their distress. Also, if the baby has a bowel obstruction, vomiting will occur--but this tends to be a very acute illness, hours to a few days--and much more severe, also relatively unlikely. For the latter, get help quickly!