These things can be observed to know whether the intellectual development of the babies is correct.
Children's development can be broadly classified into four categories - Gross Motor, Fine Motor, Language and Social. Let's check what are the milestones of intellectual development in babies.

0 - 1 month
The mother's smiling face always seen when the baby opens its eyes brings joy and hope to the babies. Make patterns in black and white (zebra lines) and show them to the baby 8 inches apart. Face the baby and have the mother talk or sing (baby likes sweet sounds like tarat).
2 month
The baby starts laughing. Mother's face begins to recognise. Hold the baby facing the mother and then play or make her laugh. Put attractive pictures on the wall. Display colored fabric or toys 8 inches apart.
3 months
Show the toys slightly above the baby while he is lying down and move them from side to side in front of his eyes. Make sure the baby follows along as you do this Look towards the sound. Take turns looking at your own hands. The baby tries to raise the head and chest while lying on the back. Listen to a variety of sounds from both sides of the baby.
4 month

The neck will be firm. Hold toys in hand and play longer. Have the ability to laugh out loud. Both hands are held together in the middle of the body and played. Show what is going on around you (cars going by, leaves blowing in the wind).
5 month
Play hide and seek. Reaching out and buying things. Making sounds. The feet touch the ground when stopped. Plays with feet. Looking in the mirror is fun. Follows with the eyes as the ball or toy rolls in front of it.

6 months

Encourage them to look at small objects. Show them colored pictures and books. Talk to the baby through facial expressions. Makes sounds by imitating others. Sitting for a while with help. Afraid of strangers. Expressing likes and dislikes. He starts shifting things from one hand to the other.

7 months
Makes different types of sounds. Reaching things with one hand. The baby can sit without help. Recognizing familiar faces.
8 months
Likes to crawl on the ground. Responds when baby's name is called. Likes to play in water. Makes a variety of sounds to attract the attention of others. Reaching for objects/toys. Likes to twist and turn. Will sit up by himself.
9 months
Trying to hold on and get up. Likes to walk. Playing tappokti. Trying to say father, mother. Trying to point out. Each hand tries to pick up one item.

10 months
Trying to imitate. Shows interest in surroundings. Starts walking on his own. Start reacting to things. Start by saying the word 'No'. A word or two will be spoken. Different facial expressions will be recognized.

11 months

Bye-bye-tata begins to show. Starts drinking water from the cup on its own. Expresses feelings of fear and apprehension. Understands own needs. Responds to loud noises. Stands without the help of anything else.

12 months
Pointing to things. He starts walking by holding on to chairs etc. Hidden items are easily found. Looking at pictures when given name or cue. Voices, gestures, and actions will be imitated to attract the attention of others. Crying when the baby's father or mother moves away. Body parts will begin to be recognized. Will be interested to hear the story