How Are Babies Made? (Ages 10-12)

Ages 3-5 Simple Explanation

You know how every animal -- dogs, cats, birds, fish -- has babies of its own kind? People have babies too, and it all starts inside the mommy's body. A really tiny part from the mommy and a really tiny part from the daddy come together to start a new baby.

You know how you need a recipe to bake a cake? The tiny parts from the mommy and daddy carry something like a recipe. When they mix together, the recipe tells the baby how to grow -- what color eyes to have, how tall to be, and all sorts of things that make the baby special.

You know how a plant grows slowly from a seed? The baby grows slowly too, inside the mommy's tummy. It takes about nine months for the baby to get all its body parts -- a heart, a brain, tiny fingers, tiny toes -- everything it needs.

When the baby is all done growing, it is ready to come out and be born! Doctors and nurses help the mommy, and then the family gets to meet the new baby. Every baby is different and special because of the special recipe it got from its mommy and daddy.

Ages 6-8 More Detail

Babies are made through a process called reproduction. It begins when an egg cell from the mother is fertilized by a sperm cell from the father. The mother's body has two ovaries that produce egg cells, and the father's body produces sperm cells. When a sperm and an egg meet and join together inside the mother's body, a brand-new cell is created.

This new cell is called a zygote, and it is the very first cell of a new person. Even though it is smaller than a grain of sand, it contains DNA from both parents. DNA is like a blueprint that tells the cell how to build an entire human body. The zygote has everything it needs to become a baby.

The zygote starts dividing right away -- one cell splits into two, then two into four, and so on. After a few days, this ball of cells reaches the mother's uterus and attaches to its lining. This is called implantation. From here, the cells start to organize and different parts of the body begin to form.

Over the first eight weeks, all the major organs start developing -- the heart, brain, lungs, stomach, and more. This early stage is called the embryo stage. After eight weeks, it is called a fetus. The fetus continues to grow and develop for the remaining months of pregnancy.

The baby is fed and given oxygen through the umbilical cord, which connects it to the placenta inside the mother. The placenta acts like a filter, taking good things from the mother's blood and passing them to the baby. By the time the baby is ready to be born, it has everything it needs to live outside the mother's body.

Ages 9-12 Full Explanation

Human reproduction begins with sexual intercourse, during which sperm cells from the father's body enter the mother's body through the vagina and travel toward the fallopian tubes. Meanwhile, about once a month, one of the mother's ovaries releases a mature egg cell during ovulation. If a sperm cell reaches the egg in the fallopian tube, the two cells fuse together. This is called fertilization, and it creates a single new cell called a zygote.

The zygote contains 46 chromosomes -- 23 from the egg and 23 from the sperm. These chromosomes carry DNA, which is the instruction set for building and running a human body. The DNA determines everything from blood type to the shape of the baby's ears. Within hours of fertilization, the zygote begins dividing. It splits into two cells, then four, then eight, doubling again and again as it travels down the fallopian tube.

After about five to seven days, the cluster of cells (now called a blastocyst) reaches the uterus and implants into the uterine lining, which has thickened to be rich with blood and nutrients. Once implanted, the cells begin to specialize. Some become the placenta, which will nourish the baby. Others become the embryo itself. Over the first eight weeks, the embryo develops the foundations of all major body systems -- the nervous system, circulatory system, digestive system, and more.

From week nine until birth, the developing baby is called a fetus. During this time, it grows from about one inch long to around 20 inches. Its organs mature and begin to function. The heart pumps blood, the kidneys filter waste, and the lungs practice breathing movements using the surrounding fluid. The fetus can hear sounds, respond to light, hiccup, and even suck its thumb. The mother can feel the baby moving, which usually starts around 16 to 20 weeks.

Modern medicine has also made it possible for babies to be created through assisted reproduction. In vitro fertilization (IVF) involves collecting eggs and sperm, combining them in a laboratory dish, and transferring the resulting embryo into the uterus. There is also intrauterine insemination (IUI), where sperm is placed directly into the uterus to increase the chance of fertilization. These methods help families who may have difficulty conceiving naturally.

By about 40 weeks, the baby is fully developed and ready to be born. The mother's body begins labor, a process where the muscles of the uterus contract rhythmically to push the baby down through the birth canal and into the world. In some cases, a surgical delivery called a cesarean section (C-section) is performed instead. After birth, the umbilical cord is clamped and cut, and the baby takes its first breath of air.