Baby's 4-month-old's Development

As I have a baby, he is not 4 months old and 2 weeks, I was browsing about the baby's development this is what I had read and learn today for 4 months old baby’s development.

Beginning to understand the role of language. The Baby can now understand all the basic sounds. Between this time and 6 months of age, the baby will develop the ability to make some vocal sounds which means you may hear the words you've been dreaming about, namely "ma-ma" or "da-da." While child development experts say it's too early for your baby to connect those sounds with you and your partner, that won't make hearing them any less exciting.
Encourage the baby to attempts communication by mirroring or imitating his expressions and sounds. He may try to imitate you now, too. Say "baa" and he may try to say it back.
Reacting when your baby makes noises or tries to say something will help your baby learn the importance of language. It'll also help him better understand cause and effect. It's great for his self-esteem, too. He'll begin to realize that what he says makes a difference.
Expand on what your baby says and try to give it meaning. For example, you can say, "Yes, that is a ball!" Soon, his "ba" will become "ball."

Time for solid food? For the first four to six months of life, your baby gets all the nutrients he needs from breast milk or formula. Still, parents are often eager to start their babies on solid food.It's true that your baby's digestive tract is more developed now and his tongue-thrust reflex is starting to fade, so it seems a logical time to start feeding him some solids, such as pureed baby food or cereal. But there are good reasons to wait, too.Starting solids later may cut down on possible allergic reactions, and ensures that breast milk or formula won't get crowded out of your baby's diet. And if you're hoping that eating solids will help your baby sleep through the night, studies have shown that you can't count on that happening.
The debate over when to start solids continues. If you're unsure about when to introduce them to your baby, talk to his doctor.