Two girls were offered for sale to an undercover agent for just over €500
Authorities in the US say 120 traffickers have been arrested as part of a major operation.
Operation Cross Country is an annual action focused on recovering underage victims of prostitution by the FBI.
The four-day operation ended October 15th, and saw 84 sexually exploited young people rescued.
The FBI says all of those recovered were offered services by specialists who are either part of its Victim Services Division, or members of other local and state law enforcement agencies.
Now in its 11th year, the operation has expanded beyond the United States - with Canada, the United Kingdom, Cambodia, the Philippines, and Thailand undertaking similar operations.
FBI Director Christopher Wray says: "We at the FBI have no greater mission than to protect our nation’s children from harm.
"Unfortunately, the number of traffickers arrested - and the number of children recovered - reinforces why we need to continue to do this important work."
This year's operation involved 55 FBI field offices and 78 FBI-led Child Exploitation Task Forces - composed of more than 500 law enforcement agencies.
Hundreds of personnel took part in sting operations in hotels, casinos, truck stops, and through social media sites frequented by pimps, prostitutes and their customers.
During operations in Denver, a three-month-old girl and her five-year-old sister were recovered after a friend who was staying with the family made a deal with an undercover officer to sell both children for sex in exchange for US$600 (€506).
"The threat of child sex trafficking is something the FBI works on every single day," FBI Denver special agent in charge Calvin Shivers says.
"Operation Cross Country gives us the opportunity to shine a light on this threat and to educate the public."
He adds that while the focused law enforcement action has "an immediate impact" of recovering a significant number of victims, "we recognise that there is a lot more work to be done to identify and recover even more victims."