Your child is now very much aware of his speech and language. He is learning about grammar and tenses at school. At home, you need to be his teacher. There are different language-improving exercises which can be practiced.
What you need to know:
At this age, you child may not be well versed with tenses. You can ask him about his school schedule, the previous day. Let your child stress his memory and then speak up. Allow him to frame his speech with tenses. Your main task is to keep a check on your kid’s sentence forming and grammar ability. You can even play a story telling game which deals with incidents of the past. Correct him whenever he makes mistakes. Mastering tenses takes time so you need to have a lot of patience. Once your child has perfected his past tense usage then you can start with future tense. This is the right age to correct your baby's grammar. You can read books aloud and highlight words that depict tense. This will also help him to understand. Play games that involve tense. This would be a fun way of learning, this crucial element of grammar.