More than 2,000 primary school-age children were arrested last year, an average of six per day, a charity has said.
The Howard League for Penal Reform said that 2,117 children aged 10 and 11 were detained in England and Wales in 2011.
Police arrested a total of 209,450 under-18s last year, down from 315,923 in 2008, the charity said. Around a fifth of the children held each year are girls.
The league has campaigned to reduce the number of child arrests on the grounds that they could lead to a criminal record for "being naughty".
Chief executive Frances Crook said: "Children who get into trouble are more often than not just being challenging teenagers and how we respond to this nuisance behaviour could make a difference for the rest of their lives.
"An arrest can blight a life and lead to a criminal record for just being naughty. The positive change in policing children will release resources to deal with real crimes.
"Only a handful of children are involved in more serious incidents and they usually suffer from neglect, abuse or mental health issues.
"A commitment to public safety means treating them as vulnerable children and making sure they get the help they need to mature into law-abiding citizens."
The figures come after a Freedom of Information request by the BBC revealed that children as young as 11 had been detained in police cells because officers thought they were mentally ill.
There were 347 detentions of this kind under the Mental Health Act in England and Wales in 2011, and two forces had held a child for more than 24 hours.