Early Signs of Autism Spectrum Disorder: A Behavioral Checklist by Age

Introduction

As parents, caregivers, and educators, we’re often the first to notice when something feels different about a child’s development. Those quiet moments of observation, watching a baby track a face across the room, listening for the first babbles, or waiting for that joyful wave goodbye, are more meaningful than most people realize. Recognizing the early signs of autism spectrum disorder (ASD) doesn’t require a medical degree. It requires knowing what to look for and trusting what you see.

This guide breaks down behavioral observations by specific age bands, from newborn to 24 months. Rather than focusing on when an autism diagnosis typically happens, we’ll walk through what to watch for at each developmental stage. The earlier families and educators recognize potential signs, the sooner children can access support that genuinely changes outcomes.

Why Early Behavioral Observation Matters

Autism is a neurodevelopmental condition, meaning the brain develops and processes information differently from a very young age. While every child grows at their own pace, certain patterns of behavior, or the absence of expected ones, can signal that a closer look is warranted.

In our years of providing early intervention ABA therapy, we’ve consistently seen one truth play out: children who receive support before age three often make remarkable gains in communication, social engagement, and adaptive skills. This isn’t because ABA “cures” autism (it doesn’t, and that’s not the goal). It’s because young brains are extraordinarily flexible and structured. Evidence-based support during this window helps children build foundational skills that benefit them for life.

Importantly, noticing one or two of the behaviors below doesn’t mean a child has autism. Development varies. But noticing several signs, or noticing them consistently over time, is a reason to consult a pediatrician or seek a developmental evaluation.

Noticing early signs in your child?

Early answers open the door to early support. If you have questions about what you are seeing, our Maryland team can help you understand the next steps.

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Behavioral Checklist: 0-6 Months

The first six months are deceptively informative. Babies this young can’t speak, walk, or play in complex ways, but they’re already communicating volumes through their faces, eyes, and bodies.

Here’s what typical social-emotional development looks like during this period, and what may warrant attention if it’s missing or delayed.

Signs to watch for in 0-6-month-old infants:

• Limited eye contact or visual tracking. Most babies start fixating on faces within the first few weeks. By 3 months, they’ll often follow a parent’s face as it moves. A baby who rarely makes eye contact, or whose gaze seems to slide past faces, may be showing an early sign.
• Lack of social smiling. Around 6-8 weeks, babies typically develop a “social smile”, a smile specifically in response to another person’s face or voice. The absence of this responsive smile by 3-4 months is worth noting.
• Minimal response to voices or sounds. While newborns aren’t expected to turn toward sound immediately, by 4-6 months, most babies will orient toward their caregiver’s voice or familiar sounds. A consistent lack of response (after hearing has been ruled out) can be a marker.
• Reduced cooing or vocal play. Babies typically begin cooing around 2 months and engage in vocal “conversations” with caregivers by 4-6 months. Notable quietness or absence of vocal experimentation deserves attention.
• Stiffness or unusual muscle tone when held. Some babies on the spectrum may feel unusually rigid or, conversely, unusually floppy when picked up. They may also resist cuddling or arching away from the caregiver’s body.

It’s worth emphasizing: at this age, signs are subtle and easy to miss. Parents often describe a vague sense of “something feels off” rather than identifying specific behaviors. Trust that instinct, it’s valuable data.

Behavioral Checklist: 6-12 Months

Between 6 and 12 months, social communication blossoms. Babies become little communicators, using gestures, sounds, and expressions to engage with the world. This is also the window where differences in development often become more visible.

Signs to watch for in 6-12-month-old infants:

• Not responding to their own name. By around 9 months, most babies will turn or look up when called by name. Consistently not responding (when hearing isn’t the issue) is one of the most commonly reported early signs.
• Limited use of gestures. Pointing, waving, reaching up to be held, and clapping typically emerge between 8 and 12 months. A baby who isn’t gesturing by 12 months may need further evaluation.
• Reduced babbling or back-and-forth vocalization. By 9 months, babies usually engage in “conversational” babbling, making sounds, pausing, and listening for a response. A lack of this turn-taking pattern is notable.
• Lack of joint attention. Joint attention is when a baby looks at something, then looks at you, then back at the object, essentially saying, “Are you seeing this too?” This skill typically emerges around 9-12 months and is one of the strongest predictors of later social communication.
• Unusual interest in objects over people. Many infants this age may show intense fascination with spinning wheels, lights, or repetitive movements while showing reduced interest in faces or people.
• Repetitive movements. Hand flapping, body rocking, or repeated finger movements that seem more frequent or intense than typical exploratory behavior can be early indicators.

In our sessions with families of younger children, we’ve found that joint attention is often the “aha” sign for parents. Once they understand what to look for, the gaze shift, the shared moment, they can immediately tell whether it’s happening regularly or rarely.

Behavioral Checklist: 12-24 Months

This age band is when many parents first raise concerns. Language is expected to emerge, social play becomes more sophisticated, and differences in development tend to become harder to overlook.

Signs to watch for in 12-24-month-old toddlers:

• Delayed or absent first words. Most children say their first meaningful word by 12-15 months and have a vocabulary of around 50 words by 24 months. Significant delays warrant attention, especially when combined with other signs.
• Loss of previously acquired skills (regression). Some children on the spectrum develop typically for the first year or so and then lose words, social skills, or gestures they previously had. Any regression should be discussed with a pediatrician promptly.
• Limited pretend play. By 18-24 months, most toddlers begin engaging in simple pretend play, feeding a doll, pretending to talk on the phone, or “cooking” with toy food. Absence of imaginative play is a meaningful marker.
• Unusual attachment to objects or routines. Strong preferences for specific toys, intense distress when routines change, or repetitive lining up of objects may be more pronounced than typical toddler preferences.
• Restricted interests. While toddlers naturally have favorites, an intense, narrow focus on one specific topic, object, or activity to the exclusion of others can be a sign.
• Sensory sensitivities. Strong reactions (positive or negative) to sounds, textures, lights, or movement, covering ears at everyday noises, refusing certain food textures, or seeking out spinning motions, often become apparent during this period.
• Reduced social interest in peers. Most toddlers begin showing interest in other children by 18-24 months, even if they don’t yet play cooperatively. A consistent lack of interest in other children is worth noting.

If you’re trying to understand the typical timeline from observation to formal evaluation, our companion post on what age autism is usually diagnosed walks through the diagnostic process in more depth.

What to Do If You Notice Several Signs

Recognizing potential signs is just the first step. Here’s a practical path forward when concerns arise.

1. Start with your pediatrician. Share specific observations, ideally with dates or examples. Phrases like “she didn’t respond to her name three times this week” carry more weight than “I think something might be wrong.” If your pediatrician suggests a “wait and see” approach but your instincts say otherwise, it’s reasonable to request a referral to a developmental specialist anyway.
2. Pursue a developmental evaluation. In Maryland, families can access free developmental screenings through the Maryland Infants and Toddlers Program for children under age three. Private diagnostic services are also available and can sometimes be accessed more quickly.

Begin early intervention as soon as possible. You don’t have to wait for a formal diagnosis to start supportive services. Many families begin parent training and structured play-based interventions during the evaluation period, which helps build skills immediately rather than losing months to waiting.

How Early ABA Therapy Supports Development

Applied Behavior Analysis (ABA) is one of the most extensively researched approaches to supporting children with autism, particularly during the early years. For very young children, ABA looks nothing like a clinical “therapy session” in the way most people imagine. It looks like play, like songs, like shared snack time, but with each interaction carefully designed to build communication, social, and adaptive skills.

We’ve seen children who started early intervention ABA at 18 months go on to thrive in preschool settings, develop strong language skills, and form genuine friendships with peers. Outcomes vary, of course, every child is unique, but early support consistently makes a meaningful difference.

For families, this often includes a combination of in-home sessions where therapists work directly with the child in their natural environment, parent training so caregivers can extend skills throughout daily routines, and sometimes daycare-based support so progress continues across settings.

Conclusion

Early signs of autism aren’t always dramatic. More often, they’re quiet patterns, the wave that doesn’t come, the name that goes unanswered, the babble that never quite starts. Knowing what to look for at each age stage equips families and educators to act early, ask the right questions, and connect children with support that can shape their developmental trajectory in profound ways.

If you’re noticing several of the signs described in this post, don’t wait. Even if your concerns turn out to be unfounded, an evaluation provides peace of mind. And if there is something to address, early action gives your child the best possible foundation.

Take the Next Step with Admire ABA

Admire ABA is here to help. Our team offers compassionate, evidence-based early intervention ABA therapy in Maryland, in-home services, parent training, and diagnostic support tailored to your family’s needs. We proudly serve families across Baltimore, Aspen Hill in Montgomery County, and Columbia in Howard County, with flexible scheduling that fits real-life routines.

Contact us today to schedule a consultation or learn more about how early intervention can support your child’s growth. 

Frequently Asked Questions

What are the earliest signs of autism in babies under 12 months?

The earliest signs in infants under 12 months often include limited eye contact, a lack of social smiling by 3-4 months, minimal response to their name by 9 months, reduced babbling or vocal back-and-forth, and limited use of gestures like pointing or waving. Joint attention, when a baby looks between an object and a caregiver, is one of the most telling early markers and typically emerges around 9-12 months.

Can autism be diagnosed before age 2?

Yes, autism can reliably be diagnosed in some children as young as 18-24 months, and sometimes earlier, with experienced clinicians. However, many children aren’t formally diagnosed until later. The good news is that you don’t need a formal diagnosis to begin early intervention services. Many supportive programs can start as soon as developmental concerns are identified.

What’s the difference between a developmental delay and autism?

A developmental delay means a child is reaching milestones later than expected but generally follows a typical developmental pattern. Autism involves specific differences in social communication, behavior, and sensory processing that affect how a child interacts with the world. Some children have both, and only a qualified evaluator can distinguish between them. If you’re unsure, a developmental evaluation is the most reliable way to get clarity.

SOURCES:

• https://www.autismspeaks.org/applied-behavior-analysis
• https://pmc.ncbi.nlm.nih.gov/articles/PMC9458805/
  
• https://www.ebsco.com/research-starters/social-sciences-and-humanities/applied-behavioral-analysis
• https://www.mindcolorautism.com/blog/applied-behavior-analysis-therapy-in-early-intervention
• https://rdw.rowan.edu/cgi/viewcontent.cgi?article=1952&context=etd