Babies kick their legs during sleep mostly because they spend far more time in light, active sleep than adults do. Newborns clock about 16 hours of sleep per day, and roughly half of that time is spent in REM sleep, the stage associated with dreaming and rapid eye movements. During REM, the brain is highly active but the body’s muscle-suppression system isn’t fully developed in infants, so all that neural activity spills over into physical movement: twitching feet, jerking legs, fluttering eyelids, and the occasional full-body startle.
Active Sleep Takes Up Half the Night
Adults spend about 20 to 25 percent of their sleep in REM. Babies spend closer to 50 percent. This difference matters because REM sleep in infants looks dramatically different from REM sleep in adults. Rather than lying still with only their eyes moving, babies can squirm, kick, grimace, and make sucking motions, all while fully asleep. This stage is sometimes called “active sleep” precisely because of how much movement it produces.
Newborns also cycle between sleep stages much faster than adults, roughly every 50 to 60 minutes compared to the adult cycle of about 90 minutes. Each transition between stages creates a brief window where movement is more likely. Since babies don’t develop regular, consolidated sleep cycles until around 6 months of age, they pass through these transition points more often per hour, which means more opportunities for kicking and twitching throughout the night.
Sleep Twitches Help Build the Brain
Those leg kicks aren’t just a byproduct of immature sleep. Research suggests they play a role in how babies wire their sensorimotor system. When a sleeping infant’s leg twitches, the movement sends a signal back to the brain, essentially telling it “this muscle is here, and this is what it feels like to move it.” Over time, these feedback loops help the brain map the body and refine motor control.
A 2022 study published in developmental neuroscience found that the characteristics of nighttime movement actually shift as babies acquire new motor skills. When an infant is learning to roll over or kick intentionally during the day, the patterns of their sleep movements change in ways that reflect this learning. The researchers proposed a model where gross motor activity during night sleep reflects ongoing movement-dependent consolidation, essentially the brain practicing and cementing new physical skills while the baby sleeps. So a baby who just started discovering how to kick during tummy time may kick more during sleep that same week.
The Moro Reflex and Startles
Some of what looks like kicking is actually the Moro reflex, a startle response present in all healthy newborns. A sudden noise, a change in position, or even the sensation of falling during a sleep transition can trigger the baby to fling their arms outward and extend their legs before pulling them back in. This reflex appears as early as 25 weeks gestational age and is fully present in full-term babies at birth. It begins fading around 12 weeks and is typically gone by 6 months.
Until the Moro reflex integrates, it can wake babies up repeatedly. This is one reason swaddling helps some newborns sleep more soundly: it contains those involuntary limb movements so they’re less likely to trigger a full wake-up. Once the reflex disappears, you’ll notice fewer dramatic startle-kicks and more of the subtle twitching associated with normal active sleep.
Gas and Digestive Discomfort
Not all nighttime leg kicking is neurological. Babies dealing with gas or reflux sometimes draw their knees up and kick in a cycling motion, even during sleep. The difference is usually context: digestive discomfort tends to come with other signs like fussiness, a hard or distended belly, arching the back, or frequent spit-up. A gassy baby who kicks at night often does the same thing during the day, especially after feedings.
Infant reflux is common and, for most babies, harmless. If your baby is gaining weight normally and seems generally content, occasional spit-up paired with some restless kicking isn’t a concern. The signs that point to something more serious include projectile vomiting, spitting up green or yellow fluid, poor weight gain, or extreme irritability after eating. These can indicate gastroesophageal reflux disease or a digestive blockage.
Room Temperature and Restlessness
Overheating is an underappreciated cause of restless sleep in babies. An infant who is too warm will often squirm, kick off blankets, and cycle their legs as their body tries to cool down. The Lullaby Trust recommends keeping the room between 16 and 20°C (roughly 61 to 68°F), with light bedding or a well-fitting sleep sack. Beyond comfort, this temperature range also helps lower the risk of SIDS, which is higher in babies who get too hot.
If your baby seems to kick more on warmer nights or when dressed in heavier layers, try stripping back one layer and checking whether the back of their neck feels sweaty. Hands and feet can feel cool even when a baby is perfectly warm, so they’re not the best gauge.
When Kicking Could Signal a Sleep Disorder
In rare cases, repetitive, rhythmic leg movements during sleep point to periodic limb movement disorder (PLMD). This condition involves brief jerks of the legs or arms that repeat in a pattern throughout the night, each lasting less than five seconds and spaced roughly 5 to 90 seconds apart. Unlike normal sleep twitches, which are random and vary in intensity, PLMD movements are stereotyped and repetitive.
PLMD is diagnosed when a sleep study shows five or more of these periodic movements per hour and the child shows clinical consequences: trouble falling asleep, difficulty staying asleep, restless sleep, waking unrefreshed, or daytime fatigue. In one study comparing children with PLMD to those with other sleep disorders, 53 percent of children with PLMD were reported to kick in their sleep, and 62 percent had leg pain or discomfort at night. The mean age in that study was about 8 years, and while PLMD can occur in children as young as 1, it is uncommon in infancy.
For most babies, the practical takeaway is straightforward. If the kicking doesn’t wake your baby up repeatedly, doesn’t come with signs of pain, and your baby is growing and developing normally, you’re watching a healthy brain do exactly what it’s supposed to do during sleep. The movements typically become less dramatic after 6 months as sleep cycles mature, REM percentage decreases, and primitive reflexes finish integrating.