Children have been arrested for pushing hard drugs including heroin and crack in almost every corner of the country, according to a report.
During 2016, at least 30 police forces in England, Wales and Northern Ireland had detained under-16s on suspicion of selling Class A drugs, figures obtained by The Independent showed.
Freedom of Information requests sent by the newspaper received responses from 35 police forces, 71% of whom had arrested children on suspicion of dealing crack, heroin or cocaine.
Suspects as young as 12 were among those arrested, its report claimed.
The revelations came as a parliamentary report said children and teenagers from middle-class families are being groomed to sell drugs by criminal gangs.
It said youngsters from "stable and economically better-off" backgrounds are at risk of being drawn in, coerced and exploited by urban crime networks.
The report from the All Party Parliamentary Group (APPG) on Runaway and Missing Children and Adults followed warnings that children are being used in a drug distribution model known as "county lines".
This typically involves city gangs branching out into county or coastal towns to sell heroin and crack cocaine.
They deploy children and vulnerable people as couriers to move drugs and cash between the new market and their urban hub.
According to The Independent's data, 22 forces were found to have arrested children under the age of 14 on suspicion of class A drug dealing offences.
Eight of the police services had similarly detained 13-year-olds, it found.
In one recorded example, a 13-year-old boy was arrested on suspicion of dealing crack and heroin in Norwich, according to the paper.
Similarly a 12-year-old boy was said to have been arrested on suspicion of possession with intent to supply a Class A drug in Dorset, but police did not recover any substances.
The APPG's paper, based on testimony given at a meeting of experts, parents and agencies earlier this year, says: "The participants of the roundtable heard that any child can be groomed for criminal exploitation.
"It affects boys and girls, children from families that experience a range of issues as well those from stable and economically better-off families.
"Some children are initially approached by their peers, who have also been groomed and exploited, which can make it even harder for them to identify the risks without prior education."
The briefing warns that children and young people who go missing from home or care are at "serious risk" of being targeted for involvement in gangs, trafficking, criminalisation, sexual exploitation and violence.
The inquiry was told that children as young as eight or nine are being regularly groomed and exploited by gangs.
It raises concerns that vulnerable youngsters who are exploited by gangs to distribute drugs are often perceived to have "made a choice" and are criminalised, rather than safeguarded and recognised as victims.