A 6-month-old girl presents to an outpatient office for a routine physical. She can sit momentarily propped on her hands, babbles with consonants, and transfers objects hand to hand. The pediatrician assures the parents that their daughter has reached appropriate developmental milestones. Which additional milestone would be expected at this stage in development?

Showing an object to her parents to share her interest in that object

A 3-year-old boy is brought in by his mother because she is concerned that he has been “acting differently recently”. She says he no longer seems interested in playing with his friends from preschool, and she has noticed that he has stopped making eye contact with others. In addition, she says he flaps his hands when excited or angry and only seems to enjoy playing with objects that he can place in rows or rigid patterns. Despite these behaviors, he is meeting his language goals for his age (single word use). The patient has no significant past medical history. He is at the 90th percentile for height and weight for his age. He is afebrile and his vital signs are within normal limits. A physical examination is unremarkable. Which of the following is the most likely diagnosis in this patient?

Pervasive developmental disorder, not otherwise specified

Childhood disintegrative disorder

A 4-year-old girl is brought to the pediatrician by her parents after her mother recently noticed that other girls of similar age talk much more than her daughter. Her mother reports that her language development has been abnormal and she was able to use only 5–6 words at the age of 2 years. Detailed history reveals that she has never used her index finger to indicate her interest in something. She does not enjoy going to birthday parties and does not play with other children in her neighborhood. The mother reports that her favorite “game” is to repetitively flex and extend the neck of a doll, which she always keeps with her. She is sensitive to loud sounds and starts screaming excessively when exposed to them. There is no history of delayed motor development, seizures, or any other major illness; perinatal history is normal. When she enters the doctor’s office, the doctor observes that she does not look at him. When he gently calls her by her name, she does not respond to him and continues to look at her doll. When the doctor asks her to look at a toy on his table by pointing a finger at the toy, she looks at neither his finger nor the toy. The doctor also notes that she keeps rocking her body while in the office. Which of the following is an epidemiological characteristic of the condition the girl is suffering from?

This condition is 4 times more common in boys than girls.

There has been a steady decline in prevalence in the United States over the last decade.

There is an increased risk if the mother smoked during pregnancy.

There is an increased risk with low prenatal maternal serum vitamin D level.

There is an increased incidence if the mother gives birth before 25 years of age.

A 3-month-old girl with an immunodeficiency syndrome has been hospitalized for 1 month due to a severe pulmonary infection. Her family came to visit her daily in the beginning of her hospital stay; however, since their car broke down they have been unable to visit for the last 2 weeks. While the infection has now been resolved with proper treatment and supportive care, the girl's nurse is concerned that the patient is becoming increasingly withdrawn. Specifically, the nurse has noticed that since the family has stopped visiting, the girl seems to shy away from contact and sometimes even becomes unresponsive to verbal or visual cues. Which of the following is most likely true about this infant's condition?

The condition can be diagnosed in adults if it lasts > 6 months

The condition is significantly more common in boys

The condition is exclusively seen in girls

The condition should be reported to state authorities

A male child is presented at the pediatric clinic for a well-child visit by his mother who reports previously normal developmental milestones. The child was born at 40 weeks with no complications during pregnancy or birth. The mother notes that the infant is able to sit without support. He is able to feed himself crackers and pureed food. He is constantly shaking his toy teddy bear but is able to stop when the mother says 'no'. Which of the following indicate the most likely language milestone the child presents with?

Saying words such as apple and cat, though limited to around 4 different words

Able to say his first and last name

Social-emotional development for USMLE Step 2 CK: High-Yield Pediatrics Lessons

Age	Milestone
2 mo	😊 Social Smile (responds to human face/voice)
3 mo	Recognizes familiar faces & objects
6 mo	Stranger Anxiety begins; smiles at mirror image
7 mo	Imitates simple sounds; enjoys mirror play
9 mo	👋 Waves "bye-bye"; plays pat-a-cake
10 mo	Plays peek-a-boo; shows affection
12 mo	Comes when called; imitates actions & gestures

⭐ High-Yield Fact: Stranger anxiety, starting around 6-7 months and peaking at 8-9 months, is a key indicator of developing attachment. Its absence past this age can be a red flag.

Mildred Parten Newhall's 6 Stages of Play

Age	Social & Emotional Milestone
15 mo	- Begins to show empathy (e.g., hugs a crying sibling). - Points to show interest.
18 mo	- Engages in parallel play (plays alongside others, not with them). - Imitates household chores (e.g., sweeping).
2 yrs	- Copies adults and older children. - Shows increasing independence and defiance.
3 yrs	- Begins cooperative play & takes turns. - Knows own name, age, and gender. - Shows a wide range of emotions.

Focus shifts from parallel to cooperative, imaginative group activities. Children learn to share, take turns, and form friendships. Managing emotions in a social context is key.

Age	Social & Emotional Milestones
3 yrs	- Takes turns in games - Shows affection for friends - Understands "mine" & "his/hers"
4 yrs	- Cooperates with other children - Engages in fantasy/role-play (e.g., "Mom," "Dad") - Prefers playing with others over playing alone
5 yrs	- Wants to please & be like friends - Agrees with rules - Shows more independence

⭐ Cooperative play emerges around age 4, where children work towards a common goal (e.g., building a fort). This is a key shift from the parallel play of toddlers.

Abnormal Development - 🚩 Red Flag Alerts

Persistent poor eye contact or failure to respond to name.
Lack of interest in other children or imaginative play.

⭐ Any regression or loss of previously acquired language or social skills is a major alert for Autism Spectrum Disorder (ASD).

High-Yield Points - ⚡ Biggest Takeaways

Social smile appears at 2 months, a key early milestone.

Stranger anxiety emerges around 6-8 months.

Separation anxiety begins at 9 months, peaking at 15-18 months.

Parallel play (playing alongside, not with) is characteristic of a 2-year-old.

Cooperative play and sharing begins around 3-4 years.

A firm sense of gender identity is typically established by 3 years.

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