Question posed to Shaykh ‘Uthaymeen, rahimahullah:
Q. My brother dresses his four year old daughter in a veil and says, “He who grows up upon something grows old upon it”, and he tries to force this upon my children. Whereas I disagree with him in this, and say to him, when they reach their menses. What is your opinion about this severity by which he has chained the childhood of this child at the age of four? May Allah reward you with good.
A. There is no doubt that your brother’s statement is the common occurance: He who grows up upon something grows old upon it, this is why the Prophet, salallahu ‘alayhi wa salam, has ordered the one who reaches the age of seven years to perform the prayer, even though he is not yet responsible for his actions, rather this is an order than he be accustomed to it.
As for a young girl, there is no ruling concerning her private zone, it is not obligatory upon her to cover her face, neck and hands or feet, and it is not befitting that she be forced into this. Whereas if she reaches a stage at which men start to become attracted to her, then she should wear the hijab to prevent trials and evil. This varies with different women, for there are some who develope quite rapidly, while others are the opposite of this. Allah is the One Who gives success.
Shaykh Ibn ‘Uthaymeen
[Fataawa Manaar al-Islaam: 3/810]
From the book “Islamic Fataawa Regarding the Muslim Child”, page 153