About 2 million children are captive in sex trafficking around the world, according to the group Operation Underground Railroad.
Thursday is World Day Against Trafficking Persons.
About 100 came out to the "Rise Up For Children" demonstration and march on the Yellowstone County Courthouse Lawn in downtown Billings.
Organizers say COVID-19 and stay-at-home orders have led to an increase in trafficking because children are spending more time on the internet.
Operation Underground Railroad works with police and other government agencies to help find children in these very dangerous situations.
After getting rescued, these children often face difficult challenges in recovering.
"The sexual trauma lasts all throughout their life," said Erin Walker of the Montana volunteer team for Operation Underground Railroad. "And especially if child exploitation materials made for them and disseminated on the internet, it's a trauma that keeps coming and it never ends. There are many things that we can argue about but the one thing that we can all get together behind is protecting children. We can all get behind that."
Operation Underground Railroad started in 2013.