Teachers have been told to encourage children to speak their first languages in their first few years of education, rather than sticking solely to English.
The Education Review Office, in a new report on oral language development for children under 9, says speaking more than one language is "a proven advantage in any language learning".
It recommends that early childhood centres and primary schools should employ staff who speak their children's first languages, encourage children to work with others who speak their language, celebrate cultural events and provide some learning opportunities in the children's first languages.
But the report says there are "few guidelines in the early childhood curriculum around the importance of both home language maintenance and second language acquisition".
It also says many early childhood services don't have a systematic approach to developing children's oral language.
"ERO found very few services where teachers had a clear and shared understanding of expectations for children's oral language learning and development," the report says.
"This lack of understanding impacted on the quality of their curriculum, including the quality of interactions, resources available in the environment, and the priority given to oral language in planning, assessment and evaluation processes.
"Often the main focus of the service was limited to issues or concerns related to speech."
The report, based on evaluations of 167 preschool centres and 104 primary schools, comes in the wake of recent research finding that an increasing number of school entrants aged 5 and 6 "have difficulty expressing ideas fluently and coherently in oral English".
Auckland University researcher Dr Jannie van Hees found that children were "spending too much time in front of the digital devices" and not enough time talking with other children and adults.
In Auckland, the report says an added challenge - and an opportunity for language learning - comes from the 160 languages spoken by the 39 per cent of Aucklanders who were born overseas.
"Diversity of first languages is rapidly increasing, particularly in Auckland," it says.
"This provides us with new and exciting opportunities to extend the range of languages spoken by all children."
The report recommends that the Education Ministry should develop "a more coherent and systematic set of curriculum expectations, assessment tools and resources for oral language in the early years [0 to 8 years]".
It also advises early childhood centres and primary schools to develop more systematic practices to "notice, recognise and respond to the linguistic strengths and needs of all learners".