There are different stages of language acquisition, from babbling to forming complete grammatically correct sentences. Obviously the first stage is babbling which starts when the child is an infant as young as two weeks old. An infant can babble consonant sounds which are voiced and unvoiced; at this stage it is all the infants is able to do.
Around 6-10 months the child’s babbling is more advanced and the child is more likely to babble sounds that he hears in his own linguistic community. Where as just a month or two younger he is babbling the same sounds as other infants not in his linguistic community.
At about one year old a child is realizing that certain words belong to certain items. They are able to say their first words and connect them to an item, which is giving them a base component to phrase structure.
Children around the age of one and a half grasped the concept of phrase structure and rules, but has not yet acquired the ability to use it. They can put together tow word utterances to tell you what they want, but cannot tell you what they know.
Around two years old children have about 400 words in his vocabulary and their MLU is about 1.75. The child has still not moved on completely to deep structure but
A Creole is an elaborated pidgin brought into brought into a full-blown language. Children of slaves from different nations came up with the Creoles so that they could communicate with each other. The reason researchers use pidgins and Creoles to argue innateness is because they all worldwide pidgins and Creoles have the same sentence structure.