Encourage Your Kids to Discover New Words by Themselves
Language skill is something that is developed over the years. It is a skill that you cannot develop in a day or two. But, the process needs to start now, in the current stage your child's development is in. One of the best ways of going about it is, making sure that you give your child ample age appropriate reading materials to start with.
Engage him in a lot reading and writing activities so that your child starts learning in a fun way. Also, encourage him to create stories so that he is able to use what he has learnt while reading the books. To develop his vocabulary, you can teach two new words every day and ask your child to use these words in writing or in daily conversation.
Over the time, when you keep doing this, slowly, you will be able to understand that your child's language skills are getting polished and he is able to express himself well.