Your kiddo at this stage is full of energy and vigor. 3 to 4 years is the best age to learn new things to store them in their subconscious mind. Things taught at this age keep up a lifelong friendship with the brain. Why not take advantage of it? The best and foremost in this context to work on is increasing your kid's vocabulary.
What you need to know
This is an ideal time to start working on your child's word bank. Try to enhance their interest in new words. The best way is to start with easy words. Teach them these words in a story form. This will help them to remember their application and correct use.
Once they are comfortable with one word then teach them the next and so on. Making it a regular exercise will help your kid to improve their vocabulary in an effective way. You can figure out a good time in your daily routine where both of you can sit leisurely and learn new words.