They've banded together in recent weeks to warn parents about the Child Evangelism Fellowship's Good News Club, buying a full-page ad in the local alternative weekly to highlight the group's tactics.
"They pretend to be a mainstream Christian Bible study when in fact they're a very old school fundamentalist sect," said Kaye Schmitt, an organizer with Protect Portland Children, which takes issue with the group's message and the way it's delivering it.
CEF says Protect Portland Children is a shadow group run by atheists who seek to dismantle Christian outreach. The group said its methods are above reproach.
"Children are easy to manipulate, we all know that," said CEF's vice president Moises Esteves. "We don't use any of the schemes and high-pressure tactics that we're accused of. Nothing could be further from the truth."
Esteves' group decided to hold its annual summer mission program in Portland because of the area's irreligious leanings.
Trying to reach young people in Oregon presents the group with two strongly secular demographics.
Gallup polls in 2008 and 2012 have consistently indicated that Oregon is among the least religious states in the country, with one of the fewest populations identifying themselves as "very religious."
Furthermore, focusing on young people opens the group up to an increasingly irreligious demographic. Millennials, or those born in or after the early 1980s, are the least religious generation in U.S. history, according to Pew Research.
CEF has encountered controversy before.
It won a 2001 U.S. Supreme Court case that decided they could hold chapter meetings on school grounds.
The organization was also the subject of a critical book that asserts the group advances a fundamentalist agenda and uses public spaces like schools to make children believe such views are endorsed by authority figures.
In schools, the group obtains permission slips to speak with children, but it is not required to do so in public spaces.
CEF spent last week training its volunteers, Esteves said, and will span out through the area this week trying to reach children.
"We do teach that children are sinners, but we're not nasty about it," Esteves said. "If we were nasty about it, the kids wouldn't come back." He said that they don't try to coerce the children, as "coercion leads to false conversion."
At a park on Monday, the group laid out a tarp for children and chairs for their parents. A pair of volunteers led about 12 kids through Bible verses and songs that praised a Christian god.
"My heart was dark with sin," they sang, "until the savior came in."
Mia Marceau, a mother of two in the Portland suburb of Vancouver, Washington, said she was intrigued when the group approached her apartment complex pool last week. She said she, too, believes in Jesus Christ.
Within a few hours, however, she didn't like what the group was telling her 8-year-old son and his friends: They were headed to hell, needed to convert their friends and were duty-bound to raise money for the organization.
"I raised a free thinker," she said. "He didn't buy in. All of a sudden, he's having arguments with his friends over salvation."
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