Okay kiddo, have you ever heard of something called chromosomes? Well, these are like tiny pieces that make up who you are as a person. Typically, girls and boys have different numbers of chromosomes. A girl has two X chromosomes while a boy has one X and one Y chromosome.
Sometimes, girls can have something called Turner syndrome which means they only have one X chromosome instead of two. This happens because of a funny way that the chromosomes are made when the baby is growing inside the mommy's belly.
Turner syndrome can cause some differences in how the girl looks and feels compared to other girls. For example, she might be shorter than other girls her age or not have started her period yet. She might also have a hard time with math or certain other things in school. But don't worry, there are lots of ways to help take care of girls with Turner syndrome so they can grow up to be happy and healthy just like everyone else!