Two Christian summer camp organisers were detained in China last month on the charge of "indoctrinating minors with superstitious beliefs".
Zhou Yanhua and Gao Ming, members of Yining County Church in Xinjiang region, had been getting ready to drive a group of children to a Christian summer camp.
Just as they were about to leave, police turned up, took the two women into custody and also took the children to the police station to register their identities.
An elder from Yining County Church, Xie Xianhua, said officials also called the families and school teachers of the children involved, threatening to deduct the teachers' wages or keep the students from being admitted to higher grade levels, according to the human rights organisation China Aid.
Gao, 27, who is a student at Yanjing Theological Seminary, was held behind bars for 15 days.
Zhou, the head of the church sponsoring the summer camp, was held for 10 days.
Chinese law forbids religious instruction being given to anyone under 18. It is held to be brainwashing.
Christian parents and church leaders can get into trouble with police if they involve their children in any Christian activities, according to China Aid.
"Gao's status as a student at an official, government-sanctioned seminary reveals that not only house churches are at risk for government suppression. Members of China's official Protestant church, the Three-Self Patriotic Movement, are also targeted," the charity reported.
A conversation took place on the Chinese messaging app WeChat between other students at the seminary.
China Aid translated some sections, where students prayed to "strengthen the faith of the co-workers, strengthen the church and also protect the children could continuously follow the Lord".
One student seminarian said: "Also, pray for the parents and the kids. It is common to be detained because of things like this."