"These schools have one aim: to send their graduates back to Christian-majority Papua to spread their muscular form of Islam."
For some of these children, who may be as young as five, it's only when they arrive that they find out they have been recruited by "pesantren", Islamic boarding schools, where time to study maths, science or language is dwarfed by the hours spent in the mosque. There, in the words of one pesantren leader, "They learn to honour God, which is the main thing." These schools have one aim: to send their graduates back to Christian-majority Papua to spread their muscular form of Islam.
For about 50 years, a separatist insurgency has been active in Papua and hundreds of thousands have died in their efforts to gain independence for the province. Christianity, brought by Dutch and German missionaries, is both the faith of a vast majority of the indigenous population, and a key part of their identity. Islam actually has an even longer history in Papua than Christianity, but it's of a gentler kind than what's preached in Java's increasingly hardline mosques and it's still, for the moment at least, the minority religion. But when the pesantren children return from Java, their faith has changed. "They become different persons," Papuan Christian leader Benny Giay, tells me. "They have been brainwashed".
The schools insist they recruit only students who are already Muslims, but it's clear they are not too fussy. At Daarur Rasul, I quickly found two little boys, Filipus and Aldi, who were mualaf - brand new converts from Christianity. One radical Islamic organisation, Al Fatih Kafah Nusantara (AFKN), makes no bones about its intention to convert, and to use religion for political ends. Leader Fadzlan Garamatan says AFKN has brought 2200 children out of Papua as part of his program of nationalistic "Islamicisation". "When [Papuans] convert to Islam, their desire to be independent reduces," says Fadzlan on AFKN's internet page.