When we acquire our first language, it happens in stages – we don’t just speak in full sentences from the day we’re born. We gradually acquire the skills to communicate in our mother tongue and/or other tongue. Also, we don’t have to formally learn it – we pick it up from those around us.
Those who acquire a first and second language at the same time are called simultaneous bilinguals. A sequential bilingual starts to learn their second language after their first language – typically past the age of 3. Simultaneous bilinguals acquire language in a more natural way, whereas sequential bilinguals require a more guided approach.
How well children (or adults) acquire their second / third / fourth / other language is not predictable and depends on many factors.
Either way, most agree that there are 4 or 5 stages in the process of acquiring another language, as outlined in the videos below. Although the presenters in these videos do not specifically talk about te reo Māori, the underlying principles still apply.
Other resources indicating stages of acquisition include the English Language Learning Progressions and the Stages of Second Language Acquisition by the Speech Pathology Group.