The foamy yellow vomit is called bile (stomach acids). It happens when the baby has an empty tummy. Try feeding him a snack later in the evening to keep some food in his tummy. If this doesn't happen very often it isn't anything to be concerned about. If it happens all the time and feeding him later at night and earlier in the morning doesn't help you can also give 1/2 of a tums to neutralize the acid so it doesn't cause stomach ulcers. |