Why Are Babies
So Bendy?
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The full narration of the video.
A baby lies on the bed and grabs a foot with both hands. Then pops it right into their mouth. Your turn? Plenty of grown-ups can't even touch their toes. Stranger still: a baby's kneecap isn't even bone yet.
So why are babies so bendy? Let's put a baby next to a grown-up and compare, one thing at a time. First, bones. A grown-up has two hundred and six. A newborn has close to three hundred. Many of the extras are still cartilage, the tough, bendy stuff in the tip of your ear. And lots of small pieces haven't joined up yet.
The kneecap is one of them. At birth it's cartilage, and it starts hardening between two and six. It only becomes real bone around ten or twelve. Same with the head. The skull plates have soft gaps between them, so they can squeeze a little to fit through the narrow birth canal. So a baby's skeleton is like a young sapling. It bends without snapping. Only later does it turn into hard wood.
Second, the ropes. Bones are tied to each other with strong ropes. They're called ligaments. A baby's ropes are loose, so the joints swing farther. Doctors see the same pattern again and again: the younger the child, the bendier, and it tightens with age. Why do they tighten? Scientists think the ropes are full of tiny clasps. In young bodies, many of them can still come undone, and with age they lock for good. The details are still being studied.
Third, body shape. A newborn's head is about a quarter of their length, and the legs are short and bent. The feet are already close to the mouth. So is a baby bendy everywhere? Not quite. A newborn's hips and knees stay bent. Try to straighten them, and they won't go flat. That's left over from months curled up in the womb. It's normal, and it loosens over the next few months.
So babies aren't born acrobats. It's lots of cartilage, loose ropes and short legs, all at once. Around four to six months, many babies discover their feet, grab them, and take a bite. How old was your baby the first time they chewed their own toes? Tell us in the comments.
Grab a foot,
straight into the mouth
A baby lies on the bed, grabs a foot with both hands, and pops it straight into its mouth. Now try it yourself: plenty of adults can't even touch their toes.
Stranger still: a baby's
kneecap isn't bone yet.
The kneecap starts
as cartilage
At birth, the kneecap is cartilage — the tough, bendy stuff in the tip of your ear. In most kids it starts hardening between 2 and 6, and only becomes real bone around 10 to 12.
That isn't a one-off. A baby's whole body is like this. Let's put a baby next to an adult and compare, one thing at a time.
Adults have 206 bones,
babies nearly 300
An adult has 206 bones. A newborn has close to 300. Many of the extras are still cartilage, and lots of small pieces haven't joined up yet. As the child grows, they harden bit by bit and fuse into single bones.
Soft gaps
on top of the head
The head is the same. The skull plates have soft gaps between them, so at birth they can overlap a little and squeeze through the narrow birth canal.
A baby's skeleton is a sapling:
it bends, it doesn't snap.
Only later does it turn into hard wood.
The ropes holding joints
start out loose
Bones are tied to each other with strong ropes called ligaments. A baby's ropes are loose, so the joints can swing further. Doctors see the same pattern again and again: the younger the child, the bendier, and things tighten with age. Among kids under 10, 1 or 2 in every 4 are more flexible than usual.
Why do they tighten? Scientists' explanation: the ropes are full of tiny clips. In young kids most are open clips; with age they slowly lock shut. The details are still being studied, and some experiments say this isn't the whole story.
Big head, short legs:
the foot is already close
A newborn's head is about a quarter of its body length, and its legs are short and bent. An adult's head is only about an eighth. For a baby, a foot doesn't have far to travel to reach the mouth.
Legs that won't straighten
are normal
Babies aren't bendy everywhere, though. A newborn's hips and knees stay bent, and you can't gently pull them fully straight. That comes from months curled up in the womb. It's normal, and the legs stretch out over the next few months.
Babies already move their legs in the womb — see why babies kick before birth. For another thing kids use first and swap out later, see the baby teeth episode.
looser ropes,
shorter legs.
the first time they
chewed their own foot?
Quick check
Why can a baby put its own foot in its mouth?
A baby's skeleton is a sapling: lots of cartilage, loose ropes (ligaments) and a big head on short legs. It all stiffens with age.
