Prefer to listen? Press play above to hear this episode of The WeeThrive Peds Podcast, or read the full breakdown below!
Did you know your baby’s brain builds over one million new neural connections every second during their first year of life?
And here’s the amazing part: each developmental milestone your baby achieves plays a direct role in how that wiring happens. Every roll, every reach, every wiggle—your baby isn’t just moving. They’re literally designing their brain.
As a pediatric occupational therapist and mom of three, I’ve seen firsthand how understanding these early milestones can transform a parent’s confidence and a baby’s development. Today, I’m breaking down the first three phases of infant motor development—from birth to independent sitting—and showing you exactly what’s happening inside your baby’s brain at each stage.
Why This Matters: My Personal Journey
Before we dive into the science, I want to share why this topic is so personal to me.
Our second son, August, struggled with a severe GI inflammatory condition as a baby. By three months old, he needed a feeding tube. Because of his reflux and pain, he couldn’t tolerate tummy time and spent most of his day upright.
As a result, he missed critical early milestones—rolling, pushing up on his arms, and eventually crawling on his hands and knees. Even when his health improved, his motor and speech milestones lagged behind.
Until one day, it clicked.
I realized we needed to go back and help his body and brain experience those missed milestones—especially crawling on hands and knees. Once we did that, everything started to change. His balance improved. His speech took off. He could finally walk without constantly falling.
If your little one isn’t following the “typical” developmental path—I see you. You are not alone, and there is a way to help your little one get back on track and thrive.
It starts with understanding how these milestones work together to shape your baby’s brain and body.
Understanding Developmental Milestones: The Four Categories
You’ve probably heard your pediatrician talk about milestones. These are developmental markers—skills most babies achieve around a certain age.
Milestones fall into four big categories:
- Social-emotional (smiling, making eye contact, showing affection)
- Language and communication (babbling, responding to their name, first words)
- Cognitive (problem-solving, object permanence, cause and effect)
- Motor (both gross motor like rolling and walking, and fine motor like grasping and reaching)
Today, we’re focusing on motor milestones—because they’re the foundation for everything else.
How the Brain Builds: Bottom-Up Development
As babies progress through motor milestones, their brain is building from the bottom up.
Sally Goddard Blythe, one of the top experts in infant neurodevelopment, explains that development moves from the lowest regions of the brain (like the brainstem) up toward the cortex—the thinking, planning, problem-solving part of the brain.
The House Foundation Analogy
Think of it like building a house:
Tummy time, rolling, and crawling are the foundation. They support the more complicated motor skills and higher-level learning that come later—things like running, jumping, reading, writing, and attention. Think of those as the house’s framing, electrical, and plumbing systems.
If the house’s foundation is unsteady, the house will eventually form cracks. And everything inside the house—the walls, the wiring, the systems—will be negatively impacted.
That’s why these early milestones are so important. They’re not just cute moments to capture on video. They’re building your baby’s brain architecture.
Phase 1: Intro to Gravity (Birth–3 Months)
What’s Happening
This first phase is all about adjusting to life outside the womb. Your baby spent nine months floating in a warm, weightless environment. And now? Welcome to gravity!
During these first three months, your baby is discovering what gravity feels like. They’ll spend time on their back, their side, and their tummy—and each position helps their brain learn where their body is in space.
The Magic of That First Head Lift
When your baby is on their tummy, they’ll start to lift their head. At first, you’ll see their head bobbing—just for a few seconds at a time.
It might not look like much. But that tiny head lift is huge. It’s:
- Strengthening the neck, back, and visual tracking pathways in the brainstem and cerebellum
- Teaching your baby how to work against gravity
- Wiring their brain for balance and coordination
The Grasp Reflex
You might also notice that early on, babies will grasp your finger if you place it in their palm. This is called the grasp reflex—super cute, right? But it’s actually a reflex that all neurotypical babies are born with. It’s automatic. Your baby isn’t choosing to hold your finger yet—their nervous system is just doing what it’s wired to do.
Over time, this reflex will integrate, and your baby will develop intentional grasping.
OT Pro Tip: Making Tummy Time Easy
Tummy time is exhausting for your infant. It’s like the equivalent of you or me going to a super difficult Pilates class.
One of the best ways to ensure your baby doesn’t hate tummy time is to start it from the day you come home from the hospital (as long as baby is medically cleared and supervised by a caregiver). This helps your baby get used to the position. They quickly learn, “Oh, this is just something we do every day.”
I also like to sprinkle tummy time in short sessions throughout the day, so baby doesn’t get too exhausted. Think 2 to 4 minutes, several times a day—not one long marathon session.
Want more tummy time strategies? Check out Episode 4 where I share all my best tips!
Phase 2: Rolling (4–7 Months)
What’s Happening
Now your baby starts learning how to move through space on their own. And let me tell you, it’s a game-changer!
Most babies roll from tummy to back first—that’s the easier direction. Later, they’ll roll from back to tummy, which requires more control and motor planning.
What’s Happening in the Brain
These early rolls are activating lower brain regions like the brainstem. Rolling also activates:
- The vestibular system—your baby’s sense of balance, located in the inner ear
- The cerebellum—responsible for balance and coordination
Once rolling becomes intentional—when your baby is rolling on purpose to get to a toy or to see you—the motor cortex kicks in. That’s the part of the brain responsible for planned, purposeful movement.
So rolling isn’t just about mobility. It’s wiring your baby’s brain for coordination, balance, and intentional movement.
Midline Play Emerges
During this phase, you’ll also start seeing midline play—bringing hands together at the center of their body, exploring their fingers, and batting at toys.
All of this strengthens core and shoulder stability and integrates visual tracking skills. And guess what? All of these components are key ingredients for sitting and crawling.
OT Pro Tip: Encouraging Rolling
This is a great time to get out your baby’s play arch or play gym and hang toys at your baby’s midline—directly over their chest—and also to their left and right sides at about shoulder level.
This encourages eye tracking and rolling from back to side. Your baby will start reaching for those toys and naturally begin rolling toward them.
Simple. Effective. And fun for your baby.
Phase 3: Sitting (5–9 Months)
What’s Happening
By this stage, your baby has been working out for months—building strength, balance, and coordination. And now? They’re ready for the next big milestone: sitting!
The Sitting Progression
Here’s how it unfolds:
- Your baby will transition from lying on their belly to sitting up on their own (this requires core strength, hip mobility, and coordination)
- Once they can get into sitting independently, they’ll start using their hands for balance (this is called “tripod sitting”)
- Eventually, they’ll sit tall without any support at all—hands free and ready to explore
What’s Happening in the Brain
This phase is lighting up the vestibular system, the core muscles, and the motor cortex.
But sitting isn’t just about the body. Fine motor skills explode during this phase too:
- Reaching with both hands
- Transferring objects from one hand to the other
- Exploring toys in new ways—shaking them, banging them, mouthing them
All of this hands-on exploration is wiring the brain for coordination, problem-solving, and eventually, more refined skills like feeding themselves and writing.
OT Pro Tip: Never Place Baby in Positions They Can’t Get Into Themselves
Here’s a rule of thumb that I want you to remember:
NEVER place your baby in a position they cannot get into themselves.
For example, if your baby cannot get into sitting on their own—by pushing up from lying on their belly—then we should not place them in a baby chair or prop them up with pillows.
The reason is simple: they’re not neurologically ready for that position yet. We need to give their brain more time to develop the muscles, sensory systems, and brain regions that control these movements.
Floor time beats fancy gear and baby seats EVERY TIME.
Remember: the more your baby moves freely, the more their brain grows.
Key Takeaways: What You Need to Remember
Let’s recap what we covered today:
✅ Your baby’s brain builds over 1 million neural connections per second in the first year
✅ Development moves from the bottom up—brainstem to cortex
✅ Phase 1: Intro to Gravity (Birth–3 months) — Baby discovers life outside the womb and learns to lift their head
✅ Phase 2: Rolling (4–7 months) — Baby learns to move through space and begins intentional movement
✅ Phase 3: Sitting (5–9 months) — Baby builds core strength and fine motor skills explode
✅ Each milestone builds on the one before, creating the foundation for the next through specific neural pathways
✅ Skipping one phase—like tummy time—makes the next phase that much harder
✅ “Everyday movements build bigger brains”
What’s Next: Crawling, Standing & Walking
In Episode 3, we’ll continue with Phases 4 through 6—crawling, standing, and walking. We’ll talk about how these milestones shape not just motor skills, but also attention, emotional regulation, and future learning.
You won’t want to miss it!
Free Resource: Download Your Baby Motor Milestone Checklist
Want a simple, visual guide to track your baby’s progress through all six phases of motor development?
📥 Download your FREE Ultimate Baby Motor Milestone Checklist here
This checklist covers everything from birth to walking and gives you clear markers to watch for at each stage.
Listen to the Full Episode
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References
Goddard Blythe, S. (2009). Attention, balance and coordination: The A.B.C. of learning success. Wiley-Blackwell.
About Sarah Cook, MOTR/L
Sarah is a licensed pediatric occupational therapist and mom of three boys—including one with Down syndrome. She created WeeThrive to empower parents with evidence-based tools to help their children thrive. Sarah combines clinical expertise with lived experience and is passionate about making developmental knowledge accessible to all families.
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