"The Prophet wrote the (marriage contract) with 'Aisha while she was six years old and consummated his marriage with her while she was nine years old and she remained with him for nine years (i.e. till his death)." -- Bukhari 7.62.88Go read the whole thing.
Islamic apologists in the West routinely claim that Aisha was older at the time of her marriage to Muhammad and its consummation. Here is evidence that mainstream Muslims understand otherwise, and consider child marriage to be completely justified by the Sharia.
"Fatwa: 'It Is Permissible to Have Sexual Intercourse with a Prepubescent Girl,'" from Translating Jihad, January 14:
This is another fatwa from IslamOnline.net, which again is the sixth most popular Islamic website on the internet, according to Wikipedia. As the author of this fatwa points out, this ruling is entirely based on the Qur'an and the example of the prophet, who is considered the perfect example for Muslims in all ages.