Ronald Boyajian, Erik Peeters and Jack Sporich were arrested in February by Cambodian police.
Authorities say they are the first to be arrested in the operation.
"Let their arrests serve as notice to any other person who might be tempted to evade justice by victimizing children outside of this country," said John Morton, head of Immigration and Customs Enforcement.
"Boarding a plane to a foreign land is no protection."
Authorities say Cambodia is ground zero for so-called "child sex tourism."
Boyajian, 49, of Menlo Park, is accused of traveling to Cambodia in September 2008 and having sex with a 10-year-old Vietnamese girl.
Peeters, 41, of Norwalk, was sexually involved with at least three Cambodian boys. Police say he paid them between $5 and $10 each.
Sporich, 75, of Sedona, Ariz., sexually abused at least one Cambodian boy, according to authorities.
Witnesses told police he drove a motor bike through the streets of Siem Riep, dropping Cambodian currency to attract children.
All three men were charged under the Protect Act. This law was passed in 2003, and makes it easier for U.S. prosecutors to charge people with overseas sex crimes.
U.S. Attorney Thomas O'Brien says the men are being returned to the U.S. where they could face up to 30 years for each alleged victim, if convicted.
"We believe that the sentences that they're going to be facing, should they be convicted in U.S. custody, are going to be severely stronger sentences," said O'Brien.
AP contributed to this report.