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.