Mexico City, Mexico—Between 25,000 and 35,000 under-18s have been recruited by Mexican drug cartels in the last four years, working from the cultivation stage of drug production, its sale and smuggling and even becoming involved in kidnap and murder.

The problem was highlighted earlier this week with news of El Ponchis, the 12-year-old hitman who likes to torture his victims before killing them and leaving his sisters to deal with the bodies.

"[Children] are cannon fodder,” said Nashieli Ramirez, director of Ririki Social Intervention, a children’s rights organization. “The international research shows us that on the issue of conflicts, the role of children and young people is increasing. They are the weakest link in the chain.”

The findings come in a report from the Network for Children’s Rights in Mexico, which has been submitted to the United Nations Convention on the Rights of Children (UNCRC). According to the UNCRC, the problem tallies with a general increase in the use of child soldiers globally.

A decade ago, the recruitment age for drug cartels was between 20 and 35 years, according to further studies. Now that has dropped to between 12 and 15.

Since President Felipe Calderon took power in December 2006, more than 30,000 people have been killed in Mexico drug wars. At least 1,200 of these are thought to be children. Between 30,000 and 50,000 children have been orphaned in the same period.

In Mexico, children under 14 have immunity against prosecution, even for murder, kidnapping and torture.

Meanwhile, the 300 Mexican families forced out of their home city of Ciudad Mier, Tamaulipas, are slowly beginning to return after 3,000 members of the Army, Marines and Federal Police were brought into the state to restore order. This followed a turf war between rival cartels which took over the northern state.