Let's take a wild guess at the breakdown. I'd say 5% domestic servitude and 95% sex trade.
Actually, child slaves in that part of the world are often used for agricultural labor, and as indicated by this case, forced street-begging is also common (though this was a sting, the plan described was obviously quite believable to the sellers). Girls are more likely than boys to end up in brothels (though of course quite a few boys do too), and I would think form the majority of domestic slaves too (after all, these people routinely treat their wives and daughters as households slaves). And some boys up as camel jockeys in various Arab countries, beaten into cooperation and starved so that they won't gain weight and slow the down the camels they ride in the races.