Why Do Babies Have More Bones Than Adults?

There is something so incredibly endearing about a squishy little baby. From their chubby cheeks to their chunky legs, you likely have an overwhelming desire to scoop them up and squeeze. That's why it might shock you to learn that your adorably squishy baby has more "bones" in their tiny little body than you do.

"Newborns come into this world with roughly 300 'bones,' which is almost 100 more bones than the 206 bones grownups have!" says Harvey Karp, MD, FAAP, a board-certified pediatrician and founder of Happiest Baby.

If you are like most parents, this is probably a mind-blowing discovery. But babies do have more boney pieces in their little bodies than adults do—and we are going to tell you why.

How Many Bones Does a Baby Have When Born?

Babies’ bodies need to be flexible and squishy so they can more easily pass through the birth canal. To ensure their skeleton is limber enough for the job, many of babies’ "bones" are actually made of soft and flexible cartilage, not bones as we know them, Dr. Karp explains.

"[Technically] babies have the same 206 bones as their parents; however, when a baby is born, several of the bones we consider to be one bone in an adult are not yet fused together, making the number of bones in a baby seem higher," says Lauren Hyer, MD, a pediatric orthopedic surgeon at Shriners Children’s and one of only three female pediatric orthopedic surgeons in South Carolina.

Many bones—particularly in your baby's hands and feet—are actually made of cartilage in infancy, Dr. Hyer adds. For this reason, they do not show up on an X-ray. Then, later in childhood, these boney segments will ossify, meaning they will turn into bone. Take your baby's soft spot as an example.

"Most parents are familiar with the pliability of babies’ bones thanks to the soft spots on their newborn’s skull, called fontanelles," explains Dr. Karp. "These 'soft spots' are spaces between your baby’s bones where the bones have yet to fully form. This allows your baby’s skull to squeeze through the birth canal."

Because these soft spots have not closed, people often consider them to be several different bones, when actually they are part of the same bone that just hasn't fused together yet. The smaller soft spot, toward the back of your baby’s skull, usually closes by the time they’re 2 to 3 months old, Dr. Karp says. The bigger one toward the front of the skull takes a bit longer, finally closing around 18 months old.

How Do My Baby's Bones Grow?

Babies and children are always growing. But there are times when the rate of growth is accelerated and times when it is more inactive Dr. Hyer says.

"Newborns and infants grow at a faster rate than at any other stage of development," she says. "If you sit a newborn next to a 6-month-old, the difference is quite noticeable. However, if you do the same with a 5-year-old and 6-year-old, you may not be able to tell who is older."

Essentially, this process of bone formation in babies is a replacement process, Dr. Karp explains. As your baby grows, their cartilage slowly gets swapped out by bone. In order to do this, tiny blood vessels throughout their body work to deliver blood to osteoblasts, which are cells that create the bone that will eventually cover, then replace, the cartilage, he says.

"As your little one continues to develop, bone growth is highly concentrated at the ends of many bones, where the growth plates live," Dr. Karp says. "When your little one finally stops growing, their growth plates close. Of course, bone development depends on many factors, including genetics, hormones, exercise, and diet."

At What Age Will a Child's Bones Finish Growing?

The most rapid periods of bone growth occur from birth to 2 years old, and then again around puberty, Dr. Karp says, adding: "Infants’ bones typically grow about 10 inches during the first year."

As your baby grows toward childhood, they will experience what is known as growth spurts. These growth spurts will happen at different times for different children, Dr. Hyler says. But all children will eventually go through an adolescent growth spurt.

"This is a time when their bodies are growing at a much faster rate than usual and typically is accompanied by the development of secondary sexual characteristics," she says. "After this growth spurt, the growth plates begin to close. The bones are then skeletally mature, and the body arrives at its final adult height."

The ossification process that your child's body is experiencing—where much of the cartilage in your child's body turns into bone—typically wraps up by the time your child reaches their mid-20s, Dr. Karp says. "At that point, bones can continue to change, but they do not grow any longer."

Keeping Your Child's Bones Healthy

To keep your child's bones healthy, you need to start with the building blocks—calcium and vitamin D. Nearly all of the calcium in your child's body is stored in their bones and teeth. But because their bodies do not make their own calcium, they need to get it every day from foods and drinks. Meanwhile, vitamin D is essential because it enhances calcium absorption.

"Babies get all the calcium they need from breastmilk or infant formula," Dr. Karp says. "However, breastfed babies—even partially breastfed babies—need a vitamin D supplement soon after birth in order to put that calcium to work. Infant formula contains added vitamin D, so if your baby drinks 32 ounces a day, they don't require extra D."

Once your child starts eating table food, it is important they continue to get sufficient calcium and vitamin D through a well-balanced diet, Dr. Hyer says. You can opt for a wide variety of calcium-rich and vitamin-D-fortified foods like yogurt, cheese, tofu, canned salmon, egg yolks, and beans. After their first birthday, they also can start to drink whole milk—or plant-based milk if they have an allergy.

"Also, a few minutes of direct sunlight on uncovered skin helps trigger a reaction to convert a precursor to vitamin D into its active form," Dr. Hyer says. "Physical activity also helps build bone strength in children. Bones will adapt to the stress or demands placed upon them, so the more active a child is playing, running, and jumping, the stronger the bones they are building."

A Word From Verywell

From infancy through adolescence, your child's bones are growing and developing. In fact, the process isn't complete until their mid-20s. For this reason, it is vital that you ensure they are getting the nutrition and exercise they need to build strong bones. Not only will strong bones support their muscles and protect their organs, but it also will provide them a strong foundation in more ways than one.