In this video, Robert Spencer explains that in the wake of the Nupur Sharma incident, Islam apologists have been deceitfully attempting to deny the fact that Islam’s Muhammad was married to a six year old girl and had consummated the marriage with her when she was nine.
He explains that such a reality is clearly explained in the Islamic writings that are most universally accepted by Muslims, whereas apologists are attempting to debunk the claim by referencing obscure writings that are almost never accepted as legitimate.
Spencer also explains that Muslims often emulate that behavior themselves, where it is common in countries such as Afghanistan for very young children to be married to grown men. See this article with more information about that matter, and see this recent David Wood Video about the issue.