They should also focus on the stipulations of the Jewish religion which allowed marrying a girl of three years and one day old!!
The Jewish website, Jewfaq.org, says:
“The minimum age for marriage under Jewish law is 13 for boys, 12 for girls; however, the kiddushin [betrothal] can take place before that, and often did in medieval times.,,” (JewFaq.org, http://www.jewfaq.org/marriage.htm)
The age of twelve approximates the commencement of puberty. According to Jewish Law, marriage at this age is not just allowed, but rather it is actively encouraged and fathers are advised to quickly wed their pubescent daughters.
According to many Jewish scholars, a girl should be married off as soon as she hits puberty and no later. The Jewish Encyclopedia says:
“The first positive commandment of the Bible, according to rabbinic interpretation (Maimonides, "Minyan ha-Miẓwot," 212),is that concerning the propagation of the human species (Gen. I. 28). It is thus considered the duty of every Israelite to marry as early in life as possible…Some urge that children should marry as soon as they reach the age of puberty.”
(Jewish Encyclopedia, http://www.jewishencyclopedia.com/view.jsp?letter=M&artid=216)
The Old Testament narrated the story of the marriage of Ishaq Bin Ibrahim Peace be upon them from Refka while she was just three years old. The Genesis mentioned that Ishaq was born while Sara was ninety years old. Then Abraham fell on his face and laughed, and said in his heart, «Will a child be born to a man one hundred years old? And will Sarah, who is ninety years old, bear a child?»(Genesis 17:17).
Refqa was born in the same year in which Sara died: «Bethuel became the father of Rebekah. Milcah bore these eight sons to Abraham›s brother Nahor. His concubine». In the next chapter thereof, the first paragraph, it is mentioned that: «Sarah lived to be a hundred and twenty-seven years old» i.e. Ishaq then was thirty seven years old, and Refka was just a baby.
When he attained forty years old and she attained three years, Ishaq has married her. Refer to: «And Isaac was forty years old when he married Rebekah daughter of Bethuel the Aramean from Paddan Aram and sister of Laban the Aramean». (Genesis 25:20). Talmud itself allowed making such marriage relation although the girl was just a child, as stipulated in the following teachings:
The 55th Commandment of Sanhedrin stated: «A maiden aged three years and a day may be acquired in marriage by coition». The 54th Commandment of Talmud Sanhedrin stated: «Pederasty with a child below nine years of age is not deemed as pederasty with a child above that».
The 11th Commandment of Talmud Khathoboth mentioned: «The sexual intercourse between an adult man and a young girl is something ordinary». Moreover, Saeed Rabi Joseph wrote: «The girl who attains three years and one day can make sexual intercourse»
To conclude, we close with the words of Mark E. Pietrzyk:
According to the Talmud, the recommended age for marriage is sometime after twelve for females, and thirteen for males. Marriage below these ages was generally frowned upon. However, a father was allowed to betroth his daughter to another man at an earlier age, and sexual intercourse was regarded as a valid means of sealing a betrothal. The age limit for betrothal through sexual intercourse was shockingly low. According to the Talmud, “A girl of the age of three years and one day may be betrothed by intercourse.”
(Mark E. Pietrzyk, http://www.internationalorder.org/scandal_response.html)
Therefore, in Judaism, it is not a strange issue to make a sexual relationship with a girl of three years, so why they criticized Prophet Muhammad صلى الله عليه وسلم Peace be upon him for marrying a nine year old girl.