Sussex Police arrested more children last year than all but seven other forces.
The only others to arrest more children were the Metropolitan Police, Greater Manchester, Kent, Merseyside, Northumbria, West Midlands and West Yorkshire.
Figures from the Howard League for Penal Reform set out arrest rates over the past six years among 44 police forces, including the British Transport Police (BTP).
They indicate that the number of arrests of children made by Sussex Police – which polices Brighton and Hove – has fallen from 7,081 in 2008 to 4,018 in 2013.
In 2008, 14 forces out of 43 held more children in custody than Sussex Police.
Deputy Chief Constable Olivia Pinkney, who is also the national ACPO policing lead for children and young people, said: “Sussex Police has been working hard over a number of years to reduce the number of young people brought into custody suites throughout the county.
“It is welcoming to see in the Howard League report that Sussex Police have seen a year-on-year reduction of child arrests over the past six years with just over half the numbers arrested in 2013 compared to 2008.
“We have introduced facilities where all members of the public, including young people, can be dealt with in police station interviews rooms, away from custody suites, and have their particular cases assessed.
“In addition, we introduced community resolutions in January 2011, whereby alleged offenders can be dealt with appropriately using reparative and rehabilitative work, always following consultation with the victim, in order that the most effective and appropriate outcome is arrived at.
“A great deal of this facilitated work will be away from custody suites.
“The reoffending rate for young people who have been given a community resolution is under 20 per cent, which has had a huge impact in decreasing the numbers entering the criminal justice system for the first time.
“We cannot be complacent and there is still work to be done to reduce these numbers further.
“Children should not be exposed to the custody environment other than in extreme circumstances and, while this is not always possible, we will continue to strive to reduce the number of children arrested.
“Sussex Police believes that the safeguarding of young people is a very serious matter and that the circumstances surrounding the alleged offence and victim’s wishes are taken into consideration before any arrest is deemed to be appropriate or proportionate in every case.
“We are glad for the support of the Howard League for Penal Reform in this work and will continue to work with them and share good practice from around the country.”