Your little one is moving and grooving and learning more about how their body works with each passing day. Some of your infant’s movements may seem organized; others, not so much.

Arm flapping may signal that your baby is happy or excited. In other cases, it can be an early sign of autism spectrum disorder (ASD), a movement disorder, or some other health condition.

Here’s how to read your child’s movements, what other signs to pay attention to, and when you should speak with your child’s pediatrician.

The youngest babies are still getting the hang of their limbs. Not only that, but their nervous system is also still developing. As a result, newborn motions are usually jerky and somewhat unpredictable.

In the first few weeks of life, you may notice big arm movements when baby is startled, for example. This is actually a reflex that will fade in time.

Older babies, on the other hand, move around much more. You may see your infant move both arms up and down at the same time or flap their hands at the wrists.

This repetitive motion — also called complex motor stereotypies — is sometimes associated with ASD, sensory issues, or other diagnoses.

However, it can also be observed in children without any of these conditions.

There’s no set pattern or timeline for how often your child may make these types of motions throughout a single day.

Researchers have studied arm movement duration in babies, and for those who follow typical development patterns, the duration of arm movements may be around 1.3 seconds per session.

You probably won’t have a stopwatch out to measure this at home, so you might pay attention to when and why your child flaps their arms as well as other symptoms your child may experience.

Arm flapping can be part of gross motor development. Repetitive behaviors tend to go away when a child is around 12 months old. For children with “atypical” development or health concerns, arm flapping may persist much longer, according to a 2017 study.

There are many possible reasons your baby may be flapping their arms — ranging from simple excitement to potential health concerns.

Noting any additional behaviors or symptoms can help you decode the root of your child’s movements. When in doubt, bring up your concerns with a pediatrician.

Early reflexes

Newborns have certain reflexes that are involuntary. The startle reflex (or Moro reflex) is present in most young infants until they reach around 3 months old.

If your baby is startled by a loud noise, large motion, or anything else, you may notice that both arms fly upward or outward before coming down again, often in a jerky fashion. Your baby’s arms may move up and down as the reflex passes and it may look a bit like flapping.


Colic is a condition where a young baby cries for at least 3 hours per day for 3 or more days per week, for 3 weeks or longer. A baby with colic may flail or flap their arms or legs while crying.

Other signs your baby may have colic include:

  • clenched fists
  • an arched back
  • legs drawn toward the stomach
  • seeming irritated when held

Colic usually happens when newborns are between 2 and 3 weeks old and may continue until your little one is 3 to 4 months old.


Babies may flap their hands or arms because they are excited or happy. Since they do not yet have the verbal skills to express their emotions, flapping is a physical way to show how they’re feeling.

You might even notice your baby flapping their arms if they’re experiencing any intense emotion, from happiness to sadness to anger. Flapping is a self-stimulatory (stimming) motion that provides the brain with sensory input to soothe.

While stimming is associated with ASD, most people — including babies — engage in some form of stimming (rocking, fidgeting, thumb-sucking) throughout their day.


Flapping of the hands and arms is sometimes associated with ASD.

According to the same 2017 analysis mentioned earlier, various studies link arm flapping and self-stimulatory behaviors in infancy with ASD.

Other repetitive stimming motions might include:

  • twisting of the arms
  • rotating of the wrists
  • waving
  • wiggling of the fingers

The key here is that these motions continue past infancy. You may also notice other symptoms of ASD that accompany your child’s movements, such as:

  • communication issues (lack of eye contact, not responding to name, trouble with conversation)
  • sleep difficulties
  • other repetitive behaviors (insistence on a particular routine, very targeted interests)

Motor disorders

Children who have movement disorders have difficulty moving the way they would like to. With babies, you may notice that they are unable to move a certain way or they have involuntary movements.

Possible movement disorders include things like:

  • tremors, or rhythmic shaking of limbs
  • myoclonus, or semi-rhythmic jerking muscle movements
  • dystonia, or twisting or contorted movements

Other health or learning complications

Other health concerns may also lead your baby to flap their arms.

For example, a child with Angelman syndrome, a genetic condition that affects the nervous system, may have trouble with balance and other motor skills. This may cause jerky movements of the arms and stiffness in the legs.

Remember: Arm flapping is not always a reason for concern. Even if your baby is flapping their arms as part of a stimming behavior, you may not need to do anything.

It should be safe to let them continue, unless it is distracting them from play or learning or they are harming themselves or others in the process.


Infants may flap their arms and hands when they are excited or upset.

If you notice your child is flapping in response to an emotional trigger, it may simply be a physical way to express emotions. They will likely outgrow the flapping in time.

Watch to see when and why your little one is flapping, as well as if the movement stops on your cue. If your baby cannot stop, there may be involuntary movements at play that warrant medical attention.

See a medical professional

You may want to make an appointment with a medical professional if the arm flapping:

  • becomes more frequent
  • interferes with their everyday activities (like spontaneous play)
  • becomes harmful to your little one or others

You can talk with the doctor about any other repetitive motions your baby makes, when and why you think it happens, and any other symptoms you believe may be connected.

It may also be helpful to record a video of the movements you’re concerned about and share them with the pediatrician.


Most children will outgrow arm flapping by their second birthdays. And the 2017 study mentioned earlier indicates that repetitive behaviors even fade sooner, often by the time a child is 12 months old.

If your child is in this age range, pay attention to the flapping but understand it’s likely part of your little one’s development. If your child continues arm flapping beyond the toddler years, be sure to mention it to their pediatrician.

There are a number of reasons why your baby may be flapping their arms.

If your infant is young, it may be colic or a newborn reflex that will soon fade away. Older babies are still learning so much about how their bodies work and may flap their arms because they’re overjoyed or feeling some other intense emotion.

However, don’t hesitate to contact your child’s doctor if you have concerns about arm flapping or if your child is showing any other signs of potential health or behavioral concerns.