From p.21 of the DfE Reading Framework:

Developing talk

Young children typically gain several new words a day, acquiring vocabulary at an astonishing rate. Yet by the time they start school, some children will have heard millions more words than others. The number of words a child has heard and can speak by the age of three is a predictor of later language development, so these early vocabulary gains are critically important. A language-rich environment is one in which adults talk with children throughout the day. The more children take part in conversations and discussion, the more they will understand once they can read and the more vocabulary and ideas they will have to draw on when they can write. Spoken language runs through the national curriculum programmes of study for English and all seven areas of learning and development in the Early Years Foundation Stage statutory framework.

At Folly View, we understand the importance of early oracy and building sentences using an increasingly-wide vocabulary. 

In our Early Years classes, we use WellComm, a speech and language toolkit for assessing and building language development. 

Throughout our curriculum (see here), we have identified the key words and vocabulary that we think are important to learn. Whilst our vocabulary grows the more we read, we also enhance the learning of new words with explicit vocabulary teaching. Sometimes these are subject-specific words (tier 3, see below), but also we teach tier 2 words, the language of an 'academic vocabulary'. 

Some useful links for parents: 

Building a strong vocabulary: How to help at home (written by Tracey Smith)

Education Endowment Foundation (Vocabulary)

Three Pillars of Vocabulary Teaching (written by Alex Quigley, author of Mind The Word Gap

Oxford Children’s Language: The Word Gap (OUP)