Hadith - Abu Dawud, Narrated Umm Salamah, Ummul Mu'minin 
When the verse "That they should cast their outer garments over their persons" was revealed, the women of Ansar came out as if they had crows over their heads by wearing outer garments.
The lower half of the hijab is a garment that does not show the woman's figure. Jeans and certain obvious garments do not meet this requirement.
Hadith - Abu Dawud, Narrated Dihyah ibn Khalifah al-Kalbi
The Apostle of Allah 
was brought some pieces of fine Egyptian linen and he gave me one and said: Divide it into two; cut one of the pieces into a shirt and give the other to your wife for veil. Then when he turned away, he said: And order your wife to wear a garment below it and not show her figure.
Tafseer - Alu'si, Rul-ul-Ma'ani, Vol. 22, p. 89
"Ibn Jarir Tabari and Ibn Al-Mundhir described the method of wearing the jalbaab according to Ibn Abbas (ra) and Qatadah (ra). The sheet should be wrapped around from the top, covering the forehead, then bringing one side of the sheet to cover the face below the eyes so that most of the face and the upper body is covered. This will leave both eyes uncovered (which is allowed in necessity).
Hadith - Sahih Al-Bukhari 7.713
The Prophet (saaws) was given some clothes including a black Khamisa. The Prophet said, "To whom shall we give this to wear?" The people kept silent whereupon the Prophet said, "Fetch Um Khalid for me." I (Um Khalid) was brought carried (as I was small girl at that time). The Prophet took the Khamisa in his hands and made me wear it and said, "May you live so long that your dress will wear out and you will mend it many times." On the Khamisa there were some green or pale designs (The Prophet saw these designs) and said, "O Um Khalid! This is Sanah." (Sanah in a Ethiopian word meaning beautiful).
It is unquestionable that a female must begin covering by the age of puberty. In all situations, Muslims are to use the Prophet's example for guidance. The Prophet married 'Aisha before she had reached puberty and consummated the marriage when she was approximately 9 years old. Getting married at such an age was not uncommon until recent times.
Puberty begins two weeks before the onset of the first menstrual period, i.e. this is the time in which she is capable of becoming pregnant.
May Allah swt guide each parent to adequately prepare the daughter for hijab and their other responsibilities, in time for puberty. Amin.
If a mother or father recently converts to Islam and has a daughter who has reached puberty, s/he should immediately begin covering the daughter. The parents should educate the daughter to understand and appreciate the reasons and advantages for covering as a Muslimah is instructed to. The new revert to Islam should not feel apologetic for covering a daughter who was not previously covering. It is as much of an advantage to her as to the new adult muslimah revert, and children do not always know what is best for them, so, like other decisions you make daily for your children, do not leave the issue of wearing hijab up to your children. Make the transition as a family, not you first, then just hoping the children follow suit on their own.
Bismillah Ar Rahman Ar Raheem Assalaamu alaikum wa rahmathullah wa barakatuh I agree that is is necessary to study the daleels and to come to your own conclusion about niqaab whether it is fard or mustahab not not even necessary. I studied them under the guidance of my father when I was 13 as he would not allow me to wear niqaab until I understood fully why it was necessary. That way it was MY decision and has remained so ever since then.Walaikum salaam from your sister in Islam. Aliyah.