For children, - Nargis Khatoon (sa), the Mother of Imam Mahdi (as)

Among the attributes of Almighty God are the Cherisher, the Sustainer,
the Discipliner. He is All-seeing and All-knowing, and wherever there
is a need for cherish, He cherishes. There is no doubt that good
issues, He shall put in the hands of good people. He knows who the
best is; He chooses the important issues to give to important people
among his servants, so they can accomplish it the best.
To cherish His servants and guide them to the right path of salvation,
the complete religion, and consummate the mission of prophets from
Adam (as) to Jesus (as), Almighty God created certain elite of people,
Prophet Mohammad (SAW) and his pure progeny (as), whom He made pure,
pious, faithful, faultless, and disciplined teachers and leaders of
humanity. They are the teachers who can fulfill the law of God and
nourish with their purity and piety the chosen servants of God.
Almighty Allah said about those elite people: "...and surely Allah
wishes to remove all abomination from you, ye members of the family
(of Mohammad), and to make you pure and spotless." (Noble Qur'an:
Al-Ahzab 33, verse 33)
Also, Almighty God chose from among the other nations, some pure and
chastised ladies who can be mixed with the pure waters of Imamate
(apostle hood), so that immaculate offspring will be born.
The Match Maker, makes matches, above the powers of the human?
Yes, lies the power of fate, when you thought it was astray
The beloved made it strait
Two examples can be given, one of them is Shahr Banu (sa) the eldest
daughter of Yazdegerd III, the last Emperor of the Sassanid dynasty of
Persia (Iran), who was brought from Persia (Iran) to become the wife
of 3rd Imam, Imam Hussain (as), the master of martyrs, and thus the
mother of our 4th Imam, Imam Zainul Abideen (as).
Similarly, Nargis Khatoon (sa), the daughter of a great Roman Caesar,
was chosen by Almighty Allah to become the Mother of our 12th Imam,
Imam Mahdi (as). Nargis Khatoon (sa), the beautiful princess, who was
also the descendant of one of the disciples of Prophet Jesus the son
of Mary (as), was sent to Samarra, Iraq, to become the wife of our
11th Imam, Imam Hassan Askari (as)so she can nourish in her pure
womb the shinning joule, the awaited holy spirit, Al-Mahdi (the Guided
One) the son of Imam Hassan Askari (as).