Northamptonshire Police take DNA samples from 10 children every week, figures obtained by the Howard League for Penal Reform revealed this week.
Many of the children required to give a sample will not have been charged with a criminal offence.
Under current rules, police can retain indefinitely the DNA of anyone they arrest for a recordable offence.
Frances Crook, chief executive of the charity, said: “Children who get into trouble with the police are usually just up to mischief.
“Treating so many like hardened criminals by taking their DNA seems excessive.”