Hello, R.,
Night-time vocalizations are usually a sign of subclinical epilepsy, a brain that has more difficulty than most making transitions from waking to sleep. Sleep talking and sleep walking, photophobia and sensitivity to strobing even from sunlight coming through the trees as you drive, extreme noise sensitivity are all signs to be aware of. It is more common each decade and you may never see any frank EEG changes in a sleep lab.
My daughter began sleep-talking at about 4 months also. She is 18 now, very bright, excellent adademically, sensitive musician and artist, and has grown up in a very peaceful household. She still talks in her sleep often, in partial sentences, more when stressed about something or when she eats a lot refined sugars or wheat and gluten products. We have both noticed that. A diet with good raw proteins and raw fats, like real unheated butter straight from the cow, or raw organic coconut oil, avocados, make it almost disappear.
Best health and peaceful days and nights,
A.