This is a rough estimation standard. The standard of girls 12 years old is not accurate, because girls' puberty usually begins at 9- 10 years old, and the average age of puberty is 1 1 year old, which is roughly within the range of 8- 14 years old. The whole adolescence lasts three to three and a half years, but there are also three years.
Children are in adolescence, so we must pay attention to a balanced diet, a combination of work and rest, and proper outdoor exercise to bask in the sun, which is conducive to physical development.