Many small children the genitals are touched or rub them. Traditionally, sexual taboos jumped and children were blamed for their natural need for exploration. The usual thing was to slap them or call them "dirty", for not adding some premonitions of blindness or terrible consequences, although these were expressly reserved for masturbation.
Still, if children touch each other and more if a girl does it, it is advisable to "distract them" so that they stop doing so. Actually, it is not necessary, but it is convenient to explain that people touch that part of their bodies in privacy and that it is more appropriate to do so, especially if there are people in your environment who are uncomfortably uncomfortable. Although we can always try to explain to adults that it is a natural behavior and that little by little the children understand the precise privacy. And soon, by observing us, they will understand that adults do not touch our genitals in public.
What certainly should not be done is to convey to the girl shame or disgust, or guilt. What he does is not bad, nor disgusting. Who sees it is the one who has a problem.
Today we are more tolerant and understand that touching the body, for a young child, is not a sign of any unhealthy obsession with sex, but a normal and natural expression of his need to learn and recognize himself. No doubt there is pleasure in some cases, but it is not related to sexual intercourse, but to the sensations of a healthy body.
What you have to be aware of is compulsive, continuous or expressly sexual behavior, as they can be signs of anxiety states, emotional problems or more serious issues, such as sexual abuse. I do not mean games or purely physical touches, but rather that they are permanent and that they are accompanied by explicit knowledge and attitudes not suitable for the child's age.
But if things are not flashy, what the genitals are touched Do not give more importance than if you scratch your head or foot.
