Grammar starts being acquired after utterances are segmented into words (at three years of age). This is so for logical reasons: rules of grammar apply to words, therefore words must first be available.

topic-comment structure

.car broken
.all-gone cookie

construction [subject predicate]
construction [adjective noun]

.bad girl

simple sentences
morphological forms

.Daddy said no

grammatical marking: articles, auxiliaries, prepositions, conjunctions ...

overgeneralization: maked

rarer morphological forms:

.subtler

complex syntactic constructions:

.The more stuff you write that nobody reads, the more frustrated you get.