West Yorkshire Police have been criticised for taking DNA samples from hundreds of children.
And some of the children were as young as ten, figures obtained by the Howard League for Penal Reform show.
The figures also show the force took DNA samples from 41 children every week in 2011.
Officers took swabs from 2,133 boys and girls aged 17 or under that year, including 42 primary school-age children, a dozen 10-year-olds and 30 11-year-olds.
Frances Crook, the charity’s chief executive, said: “When public money is tight and police forces are shrinking, it is disappointing to see valuable crime-fighting resources being wasted on taking DNA samples from thousands of innocent children while serious offences go undetected.
“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.”
Around England and Wales, police took swabs from almost 54,000 boys and girls aged 17 or under during 2011.
They included at least 368 10-year-olds and 1,030 11-year-olds. On average, officers took samples from 27 primary school-age children every week.
Many children required to give a sample were not charged with a criminal offence, the Horward League said.
Under current rules, police can indefinitely keep the DNA of anyone they arrest for a recordable offence.
A new law imposing more restrictions on DNA retention is expected to come into force later this year.
In 2010, officers took almost 70,000 DNA samples from under-18s, including four from children aged under 10, which is the age of criminal responsibility.