Passage: Girls typically have a female reproductive system. Some intersex children with ambiguous genitals and some transgender children, originally assigned male at birth, may also be classified or self-identify as girls.Girls' bodies undergo gradual changes during puberty. Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilization. It is initiated by hormonal signals from the brain to the gonads. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sexual organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia. Puberty is a process that usually takes place between 10 and 16 years, but these ages differ from girl to girl. The major landmark of girls' puberty is menarche, the onset of menstruation, which occurs on average between 12 and 13.

Question: When does menarche occur?
between 12 and 13