The management of sex offenders must be overhauled and a helpline set up for concerned parents, a charity has urged.
Children are most at risk from people they know, the NSPCC say
The NSPCC has warned that children are being put at risk because the system is under-resourced and inconsistent.
Many offenders never come into contact with the criminal justice system and the public does not know where to get help, it added.
But the Home Office Minister Gerry Sutcliffe insisted public protection was the government's "top priority".
The NSPCC said more could be done to support child sex abuse victims, as it estimates nine out of 10 do not receive any substantial help.
'Restore public confidence'
In response, it is calling for the introduction of a child protection advice service, such as a telephone helpline, to assist parents.
Police and other authorities needed to act quickly when a suspected offender was reported, the group added.
The NSPCC said the government had to ensure risk assessment was accurate, consistent and produced on time.
Dame Mary Marsh, director and chief executive of the NSPCC, said a contact centre could be used to report suspicious behaviour without giving out "unlimited information" about the location of offenders.
She added: "Parents want to be reassured that their children are safe from attack and that sex offenders have been risk-assessed and are being properly supervised and appropriately housed.
"However, it must be remembered that children are most at risk from people they know.
"The Government understands there are shortcomings in the existing system of managing offenders. We believe that an overhaul to give improved risk management, and better public education, will help restore public confidence."
Mr Sutcliffe said he welcomed the NSPCC's contribution to the debate, but asserted parents could be confident their children were being given as much protection as possible.
He added: "We already have a number of robust systems in place to protect children including Multi-Agency Public Protection Arrangements, disclosure of information on offenders, approved premises and community supervision.
"In addition we have overhauled the law in this area significantly tightening it, putting the safety of children at its heart."
An estimated 70,000 serious sex crimes were carried out against children between 1980 and 2001, according to a 2005 report from the National Crime Intelligence Service.