Why children have weak eyesight?

Most of the time, it could just be genetics. If your parents have very poor eyesight, most possibly the child will have poor eyesight. Also, doing activities at a young age that could harm eyesight, like watching TV up close or playing on an iPad continuously, can make eyesight worse at an older age. However, this is not always the case, for I am someone who uses a device daily but still has 20/20 vision.