Let me begin with a quote from a fatwa by the late and unlamented Ayatollah Khomeini of Iran.
"A man can marry a girl younger than nine years of age, even if the girl is still a baby being breastfed. A man, however is prohibited from having intercourse with a girl younger than nine, other sexual acts such as foreplay, rubbing, kissing and sodomy is allowed.
You need not fear that your Muslim male baby-sitter will rape your 7-year-old daughter. If he is a good Muslim he will only sodomize her. If he does force his penis into her tiny vagina he is obligated to pay for any surgical repairs that may be required. If those repairs are deemed insufficient you may work out a financial settlement to compensate you for his trivial infraction. No big deal. Muslim boys will be Muslim boys. And, after all, she is only a girl.
This practice flourishes in Muslim countries where women are ruthlessly oppressed and normal sexual development systematically suppressed. That would include the Arab world, Iran, Pakistan and Afghanistan. Deny men wholesome and natural sexual outlets and they will find unwholesome and unnatural alternatives.
The Grand Ayatollah's full ruling on marriage can be found here. The institution of "temporary marriage" appears to be designed to facilitate prostitution. A USA Today article tells the story.