How Many Bones Are Babies Born With? (Plus, Other Fun Facts!)

When I brought my first baby home from the hospital, I was convinced I might accidentally break her. She just seemed so tiny and delicate. But it turns out that babies aren’t actually all that fragile, and there’s a genius system behind why they grow and develop the way they do—including why their tiny bones take a while to fuse together. So, yes, babies may look easily breakable, but they actually have some wondrous superpowers!

For one thing, newborns are born with about 100 more bones than adults so that they can have room to grow. “This can vary a little between babies based on how many weeks they’re born and how quickly they’re developing,” points out William Wood, MD, medical director of orthopedic trauma at Phoenix Children’s.

So how many bones are babies born with, exactly? Ahead, experts break down everything you need to know about baby bones—plus, other fascinating facts about the infant skeletal system.

Key Takeaways

• How many bones do babies have? Babies are born with 275 to 300 bones—nearly 100 more than the around 206 bones adults have. Having so many bones at birth allows for baby to grow rapidly in the first few years of life.

• As your child grows, many of these bones gradually fuse together. Bone fusion can start as early as a few months old and continue as late as 21 years old.

• The clavicle (aka collarbone) is the first bone to develop, forming as early as 6 weeks of pregnancy. The clavicle is also the last bone to fully mature, around age 20.

• You can support baby’s bone health by providing a balanced diet rich in calcium, vitamin D and protein, as well as plenty of activity and adequate sleep.

How Many Bones Do Babies Have at Birth?

If you’re curious how many bones babies are born with, newborns typically enter the world with about 275 to 300 bones—significantly more than the roughly 206 bones in an adult skeleton. Of course, all babies are different, but one thing’s for sure: Your little one is packing a lot more skeletal hardware under the hood than you are.

You might be wondering where all those extra baby bones go. Well, they don’t disappear—they merge. "Many of the bones will fuse together as they get older. For example, the skull starts out as five separate bones that become one skull as they grow up,” explains Claire Shannon, MD, a pediatric orthopedic surgeon at Paley Orthopedic & Spine Institute at St. Mary’s Medical Center in West Palm Beach, Florida.

Why Do Babies Have More Bones Than Adults?

There’s a brilliant biological reason for all those extra baby bones. Babies grow at an incredible rate—their brains double in size during the first year alone—and having more cartilage and bones allows for that rapid growth and flexibility.

“The changes from cartilage to bone over time allows for bone growth from infancy into adulthood,” explains Robert Quillin, MD, a board-certified pediatrician and medical director at Pediatrix Medical Group in Fort Worth, Texas. As one example, the soft spots on baby’s head—also known as fontanelles—exist because the skull bones haven’t fused yet, which allows baby’s brain plenty of room to grow. (I was equally fascinated and terrified by my daughter’s soft spot when I first learned about it!)

When Do Baby’s Bones Fuse Together?

Baby bones don’t all fuse together at once, and different bones have individual timelines depending on their location and function. But Shannon notes that bone fusion can start as early as a few months old and continue until 21 years old. So even if “baby” is well into college, their skeleton might still be finishing up the final touches.

Fostering Healthy Bone and Skeletal Development

Growing healthy baby bones comes down to basics. “A healthy diet combined with sunshine and activity are vital to the growth of healthy bones,” says Quillin. Here’s a rundown of what experts suggest:

Healthy diet

Foods rich in calcium and vitamin D are great for growing healthy baby bones, says Quillin. Think quality sources of dairy and cheese, whole grains and eggs, which one study suggests are positively associated with bone development in childhood. “But don’t forget protein and minerals too,” adds Quillin. If baby isn’t eating solid foods yet, Shannon says your pediatrician may recommend supplementing with vitamin D drops. “For breastfeeding mothers, a diet rich in calcium, iron and vitamin D can help provide these nutrients to baby,” she adds.

Active play

All that tummy time, crawling and eventually running around isn’t just burning off energy—it’s helping build stronger bones. “The stress of activity allows muscle to put healthy strain on bones, which supports continued skeletal growth,” explains Quillin. Experts say to aim for about 30 minutes of activity per day for babies under one year old, and three hours a day for toddlers aged one to 2 years old.

Rest

Getting enough sleep plays a vital role in healthy development of baby bones, says Mitzi Williams, DPM, a pediatric foot and ankle surgeon with special interest in musculoskeletal development at Paley Orthopedic & Spine Institute at St. Mary’s Medical Center in West Palm Beach, Florida. One study even found that baby growth spurts are associated with longer sleep.

Other Fun Facts About Baby’s Bones

Are you ready for some fun baby bones trivia? Here are eight fascinating facts about baby’s skeletal system.

1. Baby’s born with a full set of teeth

You can’t see them, but they’re there! Your newborn’s primary teeth are already formed and hiding beneath the gums, just waiting for their moment to shine. In fact, baby tooth development starts in the womb at about 6 weeks, then forms that final hard shell at around week 9 to week 17 of pregnancy.

2. Kneecaps start as cartilage

Baby technically doesn’t have kneecaps—at least, not bony ones. “The patella, or kneecap, is made up of cartilage when we’re born and doesn’t develop into bone until around 6 to 10 years old,” notes Wood. This could be by design: That softer cartilage helps cushion all those falls when babies are first learning to walk. This makes me feel so much better since my one-year-old falls approximately 47 times a day—his cartilage is definitely doing its job.

3. The first bone that develops is the clavicle

As early as 6 weeks of pregnancy, the clavicle, or collarbone, starts to form, says Williams. Then, the spine follows suit.

4. The clavicle is also the last to finish developing

Plot twist—while the clavicle is the first bone to start forming, it’s also the last to fully mature. It doesn’t fully develop until you’re around 20 years old, says Wood.

5. Kids have special healing superpowers

If your little one takes a tumble (and they will—many, many times), take comfort in knowing that children’s bones heal remarkably fast compared to adults. This is because kiddos have a thick lining called the periosteum around their bones. “This lining, which resembles a thick cellophane wrap around the bone, helps nourish and develop the growing bone,” explains Wood. “It’s the magic, along with the [areas of developing cartilage], that’s responsible for the quick healing and remodeling of kids’ bones.”

6. Bones are surprisingly watery

You might picture bones as dry and hard, but they’re actually around one-third composed of water. The rest is a combination of collagen and minerals, such as calcium phosphate. “These are the materials that the bone cells used to build bone (osteoblasts) and remodel bone (osteoclasts),” adds Quillin.

7. An infant’s bones have lots of cartilage

Baby bones contain large amounts of cartilage, making them more flexible. They’re softer than adult bones and can bend before they break, protecting them from injury, says Shannon. Think of this flexibility as a built-in safety feature for those wobbly, accident-prone babies.

8. We get a new skeleton every 10 years

Bones are constantly renewing themselves throughout our lives. “Given an annual bone renewal of 10 percent, we get a new skeleton every 10 years,” says Quillin. Pretty neat, right?

To Sum It Up

Baby bones are pretty remarkable. Those 275-plus bones they’re born with aren’t a design flaw—they’re exactly what baby needs for the incredibly rapid growth they’re going through. Over time, these bones will fuse into the 206 bones of an adult skeleton, but for now, that softer, more pliable structure is serving your little one well. In the meantime, keep up all the healthy habits that’ll help baby grow strong!

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.