A very disturbing report done by Mexican newspaper, La Jornada, documents the tragedy of deporting undocumented Mexican children into Tijuana.  During the first seven months of this year, some 70,000 children were forcibly deported from the United States into Mexico.  Many of these children are unable to travel back to their home state and tend to remain on the border.  The outcome for these children is also grim according to the La Jornada Michoacán report:

The unit also estimated that 6,000 minors between 14 and 17 years old originating in Michoacan remain in the border city of Tijuana after being abandoned by the authorities of the United States. And, for those who survive, those minors are devoted largely to illicit activities. Deportation of such children has a greater impact on the states with high migration flow such as Michoacan, Jalisco, Guanajuato and Zacatecas, and involves a systematic violation of children's rights by the U.S. authorities.

Most of these children are forced to survive by begging, stealing, and squatting, lending themselves out as prostitutes and drug runners:

One of the effects of lack of child protection in transit between Mexico and the United States, is that these fall into prostitution or drug trafficking networks when they are alone.

The Registry of Migrante described the situation of 6,000 children who are abandoned in Tijuana, having failed in an attempt to cross the border, and so have opted to find work doing anything with to survive without their parents. They have become, often, victims of abuse by coyotes and criminals.

This action by the United States is in violation of the international agreement, Convention on the Rights of the Child, regarding the repatriation of migrant children.  Only adults are permitted to be deported rather than repatriated. 

De enero a julio Estados Unidos ha deportado a unos diez mil niños originarios de Michoacán -- La Jornada Michoacán (in Spanish)

En 7 meses, EU deportó 90 mil niños mexicanos -- La Jornada (in Spanish)