well it is a crime in islam to marry with kids until they are 18 than only you can marry with your moms brothers daughter no harm in it but she must be 18 not a kid it is a hilarious crime some how in cities in pakistan this is getting lower and lower with education but in villages this is still happening but now at a lower rate but in india i really dont know about it in rajhistanh ratio is bit much higher but in pakistan it is getting lower and lower but stilll it is happening in pakistan
Actually they can marry at any age in Islam. Sex is only allowed after the girl's first menstruation cycle.
Just letting you know that you are wrong.