Babbling to babies is OK, despite previous warnings against it

Talking baby talk makes child learn two languages — Never use baby talk to young children, a speech expert warned parents in London. Otherwise, the children will have two languages to learn instead of one. “If mothers could only realize what harm they do they would never talk down to a child,” said Mrs. Barbara Hicks, a fellow of speech and drama at the College of Music, London. “It’s just as easy to say ‘train’ as to say ‘puff-puff.’ ” 
— Science News Letter, January 23, 1965

UPDATE

Hicks’ advice was probably well-intentioned, but it’s wrong, says psychologist and language researcher Erik Thiessen of Carnegie Mellon University. Little work has focused on the effects of nonsense words. Still, what has been done suggests that baby talk makes words easier for babies to pronounce and teaches general language concepts. Many studies indicate that the high-pitched, exaggerated vowels of “parentese” help babies learn to form words. As for a second language being harmful, research suggests that babies from bilingual families get a learning boost over children who hear only one language at home (SN Online: 8/8/14).