Ask An Expert: When Babies Learn to Sit with Brooke Boruff, OTR/L

Brooke Boruff, founder of Infant Insights, lends us her expertise as a pediatric occupational therapist and mom who specializes in baby development.

Your little one has been hard at work these past few months, mastering tummy time and building the muscles needed to lift and keep their head and chest off the floor. They’ve figured out how to get from Point A to Point B by rolling around on the floor as means of mobility, and now, they’re working on developing the core strength needed to sit up on their own. Sitting is a huge milestone in your baby’s first year of life because it opens the door to independence and new developments. Not only is it a precursor to crawling and walking, it allows your baby to see the world from a whole new perspective.

When your baby can sit up, they can interact with their environment in new ways, engaging their senses, improving hand-eye coordination, and building fine motor skills with a stable base that makes skills like reaching and grasping easier. The ability to sit is also a sign of readiness in starting solids—-another big step forward for your little one. With so many exciting developments on the horizon, there’s a lot to look forward to as your baby grows. Here’s everything you need to know about the sitting milestone:

What age do babies sit up?

At 6 months old, your baby may be able to sit for a very brief period of time when placed in the sitting position. They may assume the “prop” sitting position, where they sit with their hands between their legs, and stabilize themselves very briefly with lots of wobbling. Around 7 to 8 months old, your baby will sit for a little longer, and will have intermittent periods of upright posture as their back muscles strengthen. Around 9 months of age, your baby will sit very well for long periods of time, and will begin to show signs of transitioning themselves into sitting from the floor or from sitting to the floor. At this age, they may also exhibit a protective response by putting one arm out to catch themselves if they begin to fall. 

However, the typical age for sitting changes depending on where you live in the world. In the United States, we sit our babies upright before they are able to sit themselves. In other countries, parents typically wait until their babies can put themselves into a sitting position (with the exception of feeding seat usage). 

When should I be concerned if my baby isn’t sitting?

If your baby is not sitting well at 8 or 9 months old, you may want to consult their pediatrician. At this age, your baby should sit with a tall posture for a prolonged period of time, and at least rotate at the trunk in attempts to reach toys in their surroundings. This delay may be due to low muscle tone, and purposeful play can help your baby get back on track.

What causes delays in sitting?

Babies who struggle with sitting skills often have one of two difficulties: low muscle tone or unbalanced muscle tone. In sitting, the whole core should be engaged and developing in order to achieve tall, upright sitting. If your baby has low muscle tone, they may appear to fall over very quickly with little to no wobbling noted in sitting. They also exhibit a very folded posture because the back core muscles are not engaged. With the implementation of activities to strengthen the core muscles, sitting skills should improve in neurotypical babies. 

When a baby has unbalanced muscle tone, they may often fling back in a sitting position. This backwards falling is due to the back muscles being much stronger than the front core muscles. The core muscles must engage equally to maintain an upright and balanced sitting posture, so if the baby is often falling backwards, front core muscle strengthening exercises may be helpful. This unbalanced muscle tone in sitting is often seen in babies who have high muscle tone and/or have a history of torticollis or full body tension.

Although it’s not guaranteed, delays in sitting may lead to delays in standing and walking. If sitting delay is due to low muscle tone, the muscles that are needed for standing and walking may also be weak. Low muscle tone is a domino effect, and can affect all muscles in the body. It’s important to seek help from a provider if you are concerned about delays.

How does tummy time help with sitting?

Tummy time is crucial in many areas of development. When an infant is laid prone on the floor, they have to develop muscles in the back, chest, and arms in order to prop and lift their heads up against gravity. All of these muscles that are developing in tummy time directly connect to the muscles required in sitting. Arm strength is crucial in prop sitting, protective responses, and transitioning skills. Back muscles and front abdominal strength are important for upright sitting posture.

How does sitting affect development? 

Sitting lays muscle strength foundations needed for crawling, standing, and walking. Core strength is crucial in movement and sitting lays those foundations. Sitting also allows your baby to interact in different ways with their environment, which encourages learning, curiosity and overall development. 

How can I encourage independent sitting?

To encourage your baby to sit, try these exercises at home:

• Baby sit-ups: Lay your baby on their back, facing you. Bring your baby slowly up to a sitting position by placing your hands behind their shoulders and lifting them up. Go slowly to make this activity more difficult, and make sure to stop the activity if you see a lot of head lagging. This activity is recommended for babies who are 5 months old and have strong head control.

• Baby tornados: Place your baby on their back with your hands behind their shoulders, then bring your baby up to the 45-degree angle. At that position, rotate your baby in small circles to the left and then to the right to encourage all parts of the core to engage. Stop this activity if you see head lagging and avoid performing this with babies younger than 5 months or babies who have weak head control. 

• Sitting with a large toy between the legs: This position encourages your baby to keep their legs wide and also offers some support for them to lean on if needed.