See a video about Marriage and Sex in Islam. Not sure about the legitimacy of these funny rules in Islam.
Still they are in the old age. Closing the eyes and calling the world is DARK
An Example: A father has a 9 year old daughter (I like to call her a kid) and if the father has to go for a trip then the Islam is suggesting him to marry her to someone. May be an acceptable rule few hundreds years back. I am assuming that there are no facilities to plan like now.
Think about a girl getting married to someone at 9.