The law, brought in on April 4, 2011, allows worried parents to find out whether people in contact with their children - including new partners - have a criminal record.
It was named after Sarah Payne, who was murdered in 2000 aged eight by paedophile Roy Whiting.
Her mother Sara, who campaigns on child protection issues, has now praised the results.
She told the Sun newspaper: "If just one child has been kept safe as a result of Sarah's law then all the work to see it introduced would have been worth it.
"The fact that it is hundreds of children is wonderful and testament to the fact the scheme is needed."
Home Secretary Theresa May said: 'Thanks to Sarah's Law, we know that more than 200 children have been protected from potential harm over the last year.
"We are doing everything we can to protect the public, and especially children, from predatory sex offenders by tightening the law and closing loopholes. But families themselves have a vital role to play.
"It is important that parents, guardians and carers are aware of the disclosure scheme and their right to request information if they have concerns."
Jon Brown, the head of the NSPCC sexual abuse programme, said more than 60 children being abused every day.
He told the Sun: "The Government has to start treating the situation as seriously as they would if faced with an outbreak of chronic disease.
Those wishing to make an application under Sarah's Law are encouraged to make enquiries with their local police force.