The amazing thing to note is that even for human children, the rules of grammar and syntax don't all fall together at the same time. Words that they are said properly one day may suddenly change as they add new rules to their mental lexicon and learn to apply them. While they are on their way to perfecting their linguistic skills, they are listening, watching and learning to comprehend the world around them. As in prehistoric man, maybe comprehension comes first. The left hemisphere of our brain is specialized for verbal or analytic processing.
Humans attend to language sounds from birth.
Apes have not as yet mastered our language. I'm not sure that they will ever do so. Genetically, chimpanzees and bonobos are very closely related to us. In some studies that have been done, chimpanzees have been brought into a human household with the express intention of giving them the same advantages of a human child in learning language. But if the human fetus start listening while still in the uterus, then an infant chimp brought into a human home may be at a disadvantage from the start.