The National Unity Government (NUG), a shadow government set up by opponents of last year’s coup, said that some of the children held were under 12 years old and some younger than five, accusing the army of a “grave violation” of international law.
A member of the area’s People’s Defence Force said that most had been released by Monday morning when troops withdrew, but some adults were arrested.
“We could not fight the troops as they were holding the children,” said the militia member, who asked not to be identified.
The junta has labelled the NUG and the people’s defence forces as “terrorist” groups.
The military has been accused in the past of using civilians as human shields and for taking over schools and monasteries to use as bases.
Phil Robertson, deputy Asia director of Human Rights Watch, said such events showed that the military was operating with “total impunity”.
More than 1,500 people have been killed in a crackdown by Myanmar’s security forces since last February’s coup removed a government led by Aung San Suu Kyi, according to a Thai-based activists group.
The military, which has disputed the death tally, is also fighting on multiple fronts with armed pro-democracy groups in the countryside and ethnic minority forces.