The couple and two Brazilians suspected of helping them were arrested at the Colina do Sol nudist colony in the state of Rio Grande do Sul.
"We started investigating the American couple in March when we received an anonymous phone call charging the couple with sexually abusing young boys in their home inside the colony," police inspector Juliano Ferreira said by telephone. "The arrests were made after some of the victims came forth and told us their stories."
He said that Louderback is suspected of sexually abusing at least 10 boys between the ages of 6 and 14, all from poor neighborhoods near the colony. Louderback's girlfriend, he added, lured the boys with promises of gifts, food and trips.
Brazil's Agencia Estado news agency reported that Louderback is a former military jet pilot and that the couple's lawyer denied the accusations.
"It's a misunderstanding that will be cleared up," said the lawyer, Paulo Alves.
Footage aired by the Globo TV network showed a man identified as Louderback, shouting at reporters who accompanied police making the arrest.
Ferreira said Brazilian detectives received assistance from the FBI on the case and also seized laptops, photographs, a camera and DVDs.
Most of the roughly 100 families living in the colony are Brazilians, Ferreira said.
