Heathcliff

To an extent, things like "baby want milk?" also help with language acquisition. We could say "would my baby like to have a drink of milk?", and that would give exposure to a lot more vocabulary early on, but it also uses much more complex grammar and abstract concepts like "would", whereas the former phrase uses only a subject, an object, and a verb which corresponds to a thing that the baby can easily conceptualize because they "feel" it (the feeling of wanting something). It's similar to learning a language later in life - you usually start with things like "I am a boy" or "This cat likes fish", rather than "My good sir could you please enunciate better so that I might understand your foreign tongue", because it helps our brains take on the basic "shapes" and "sounds" of the language, which make learning the more complex and abstract parts easier later. As for why people do it with pets, who aren't learning a language? Idk, I guess small cute thing kicks the baby instinct into gear whether it's human or not 😂