The
stage of “developing language” begins around the age of 2 to 3 and
continues until approximately 5 years old. It is Brown’s stages II through V.

Children have MLU of more than 2 but usually not more than 5 morphemes. It is
the most explosive stage of language from telegraphic to sentence mastery. For
children with language disorders, the process of developing language is lengthier.

They may be older than 2 when they start it, and they may be at school age
before they complete it.