Mexican authorities have arrested the alleged leaders of a ring suspected of smuggling more than 100 children into the United States in the past year for up to $1 million.
They also rescued five children due to be sold.
Two suspects were arrested after they apparently smuggled six other children, all believed to be from El Salvador, into the United States, Mexico's public security ministry said.
Mexico's federal police arrested Ms Estela Barajas Gonzalez (26) and Ms Virginia Barajas Perez (43) on Monday in the airport at Tijuana, just south of the border with California.
The women raised suspicions after they arrived at the airport with six children aged 9 to 11 and booked return flights to Mexico City without the youths, the ministry said. After their arrest they led police to a house in central Mexico state, where five other Salvadoran children were found.
The children told authorities they had been promised they would be reunited with family members in the US or told they could have a better life there, the ministry said.
The ring also is suspected of previously selling children from Honduras, Guatemala and Mexico, a ministry spokesman said.
Police do not yet know why the children were being smuggled, but they have not ruled out organ-trafficking and child pornography as possible motives, the spokesman said.