A baby's brain grows more during infancy than at any other time, doubling its volume and reaching approximately 60 per cent of its adult size by 1 year. As baby's brain grows, nerve cells, or neurons, grow, too. These neurons connect to make circuits, which allow baby to think and act. There are common developmental milestones that a baby should reach as he grows: For example, by 3 months, baby should recognise his caregiver's face, voice and scent. A parent or caregiver can help baby develop intellectually, first by understanding what baby's capable of learning at various ages, and second by engaging in activities that help baby learn.
Birth to 3 Months
At this age, a baby builds her memory, particularly short-term. She can focus most easily on objects between 8 and 14 inches from her eyes, usually the distance her mother's face is his while she nurses. After a month or two, she'll begin to use sounds to express herself and to get attention.
Babies like to look at high-contrast colours. This is because they're easiest to see. Black, white and red are perfect choices for baby toys, mobiles or playmats.
Carry baby in a sling or carrier, not only for bonding purposes, but also for intellectual stimulation. Because baby will be up at his caregiver's level, she will be involved in a wide array of activities, and will hear, see and feel much more than if she were in a playpen or crib during that time.
Creating a stable daily routine will help baby trust his environment. That's an important foundation, because from there, she can later learn to predict events in it, and manipulate it herself.
Talk to your baby: While she can't yet respond in actual words, she is listening to the rhythm, tone and different sounds of your language, and mentally filing them away for future use. Use "motherese" at this age -- speaking slowly and distinctly, using exaggerated facial expressions, and raising the pitch of your voice. Talking like this will engage your baby and capture her attention.
3 to 6 Months
Baby will be babbling now, and may even say "mama" and "dada," though he may not necessarily be referring to you. Help baby's language development by imitating the sounds he makes: This will show him that you are listening, and that he can use language to make himself heard.
Baby will also be discovering his arms and legs. He can now grab and shake objects. Give him a rattle or a ball with a jingly bell inside, and show him how to shake it and make noise. This teaches him cause and effect. You can also attach little rattles or noisemakers to his ankles and show him how to kick so that they make noise. Then lay him on a playmat and dangle some toys above his head. He'll swipe at them and try to grab them, building hand-eye coordination and depth perception.
Babies at this age love mirrors. Put baby in front of a full-length mirror and watch him smile at his reflection. You can also give baby a small, unbreakable toy hand mirror to play with.
6 to 9 Months
Peekaboo is a favourite game for babies of this age. They're just beginning to understand object permanence: Even when an object is out of their sight, they can still retain an image of it in their minds rather than forgetting about it completely, which is what they did earlier in development.
Give baby plastic containers of various sizes. He will be fascinated by how the smaller ones fit into the larger ones. He's learning about dimension and space. You can also encourage this intellectual skill by giving him stacking toys, and blocks with which he can build small structures.
Another way to teach baby about dimension and relationships between objects: Let him "help" with the laundry. He'll probably take it all out of the basket and put it on the floor. Then show him how to put it all back in again.
9 to 12 Months
Hide-and-seek will exercise her short-term memory. Hide a toy under a blanket and ask her to find it again. You can also go hide behind a piece of furniture and call her name. She'll follow the sound of your voice to come find you.
By 1 year old, baby may be saying her first words. You can help her by pointing out and labelling everyday objects in her world. For example: When the cat comes into the room, point, wait until baby looks, and say, "Cat!" This will help her associate the word with the animal.
You can also begin associating gestures with words: For example, when bidding farewell to a playmate, say "Wave bye-bye!" and wave your hand. Soon, she'll imitate you whenever it's time to say goodbye to someone or something. You can also take this a step further and teach her sign language for basic concepts. This will help her to express herself when she's still shaky with words. "More," "all done," and "milk" are popular signs to teach babies.