Essex Police has apologised for a catalogue of errors involving 30 child abuse investigations.
Most of the cases highlight the problems of "effectiveness" in cases carried out by the child abuse investigation team covering the north of the county.
Chief constable Stephen Kavanagh said: "Recently our teams have discovered the consistency and effectiveness of some cases of the child abuse investigation team in the north of the county are not where we would want them to be.
"Rightly we have now referred all those matters to the Independent Police Complaints Commission."
He added the force was determined to find out what has happened and to "rectify things quickly, not least for the victims".
Deputy chief constable Derek Benson said: "We have contacted the families of those involved in these investigations to let them know what is happening and apologise for the undoubted distress this has caused them."
Essex Police said a recovery plan has been put in place and steps have already been taken, including new officers taking over the investigations that have caused concern.
Other actions include an experienced senior retired detective being brought in from outside to review the investigations in the north of Essex and new monitoring systems being put in place across all of its child abuse investigation teams to closely assess the workloads of officers and ensure none of them are stretched too far.
Shy Keenan, a spokesman from Phoenix Post, an advocacy group for victims of paedophilia crimes, tweeted the police and Essex Council and CPS jointly had "a lot to answer for going back much further than 2011".