When does a baby say its first words, Mama and Dada? When does a baby learn to stand up and walk on its own? Is it normal for an infant to develop stranger anxiety at 9 months? In this quick and easy-to-understand lesson, we review the infant developmental milestones at 1 month, 6 months, 9 months, 12 months, 2 years, 3 years, and 4 years. This lesson includes high-yield USMLE quick take-home points, high yield summaries, and practice test questions/answers on infant developmental milestones.

At 1 month, the baby should reach the following main developmental milestones:

• lift head
• track with eyes
• recognize parents
• coo

Memory Aid: Think of the logic behind the order. Baby lifts its head. Eyes wander and then sees parents! Coos at (parents).

At 6 months, the baby should reach the following main developmental milestones:

• sit up
• raking grasp (using palm and fingers (not usually thumb) to move objects)
• babbles (babble but can’t say Mama/words)
• stranger anxiety (anxious around strangers who are not mama/dada/or familiar caretaker)

At 9 months, the infant should reach the following main developmental milestones:

• walk with assistance
• 3 finger grasp
• Say words like Mama/dada
• Wave bye-bye/patty cake

At 12 months, the infant should reach the following main developmental milestones:

• walk with no assistance
• 2 finger pincer grasp
• Mama/Dada
• Imitate parent

1-year-old who can’t walk is fine, but a 1-year-old who can’t sit up is worrisome.

This is a commonly tested point in USMLE. High-Yield. So if the vignette says a one-year-old is brought into the clinic and has not learned to sit up yet, then there is likely a medical problem!

At 2 years, the baby should reach the following main developmental milestones:

• Climb 2 steps
• 2 word phrases
• Follows 2 step commands
• Can stack 6 blocks (2+2+2=6)

At 3 years, the toddler should reach the following main developmental milestones:

• Ride a tricycle
• Make 3 word sentences (I like you!)
• Brush teeth (think of a 3 multi-layered toothpaste!)
• Draw a circle (3.14)
• Can also draw a face with 3 parts (face, eyes, mouth)

4-year-olds should reach the following main developmental milestones:

• Can hop on one leg (looks like a 4)
• Copy a cross “+” (literally draw a cross)
• Play with kids and have fun!

High-Yield USMLE Points: Infant Developmental Milestones – Summary Table and Mnemonics

Practice Test Questions: Infant Developmental Milestones

Answers to the practice test questions are at the bottom of this article! Good luck!

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Answers to Practice Test Questions:

1. 3 years old! The child is likely 3-years-old because he has reached developmental milestones for 3-year-olds including riding a tricycle and drawing a circle. The fact that he is not yet interested in playing with other kids is indicative that he is likely not a 4-year-old. 4-year-old are more likely to be interested in engaging group play, or playing with other kids, rather than by him/herself.
2. Walk with no assistance. At 1 year, the baby ideally should know how to walk no assistance. August is 9 months old, so he/she should have already know how to sit up by him/herself and achieved new milestones, including waving bye-bye, grasping objects with 3 fingers.

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