Green MP Sue Bradford is congratulating the police for issuing an official warning to Christchurch man who flicked his son about the ears.

The man was disciplining his three-year-old after a biking accident involving his younger son in the central city.

Ms Bradford, the instigator of the anti-smacking legislation, says if an adult whacked another adult around the ear, they would be "marched down to the slammer."

She says police have used their discretion by choosing not to prosecute the man and believes a warning is the right punishment for incident. She says it shows that the law is working as MPs intended it to.

Ms Bradford says parents need to accept that it is no longer legal to hit children. She remains confident her anti-smacking laws will change what she describes as a culture of violence.