The Green MP campaigning to ban smacking has conceded that lightly smacking a child is not a crime.

Sue Bradford, aware of the strong opposition to her private member's bill, is looking for compromises without gutting it and has suggested an explanatory commentary.

But National is looking at more radical changes, such as an amendment defining reasonable force.

As worded, the bill would remove section 59 of the Crimes Act, which says parents are "justified in using force by way of correction towards a child if that force is reasonable in the circumstances". This can be used in a legal defence.

Ms Bradford's Crimes (Abolition of Force as a Justification for Child Discipline) Bill has been widely interpreted as an anti-smacking move. The Greens call it an anti-beating measure.

"I've always been open to changing the wording of my bill or the commentary," Ms Bradford said last night.

"What I'm not willing to compromise on is the definition of reasonable force and saying we should define what nature of force is reasonable against children."

She said the justice and electoral select committee, which starts hearing submissions on the bill tomorrow, could write a commentary to accompany it.

"We could ... say as part of the commentary that it's not our intention to criminalise parents for putting their children into a room for time-out or for physically removing them from danger or for lightly smacking them - which are all the things that the bill has been accused of doing."

Another option was to reword the bill, but she was not offering any alternative wording, preferring to wait to hear from submitters.

More than 1700 submissions have been received on the bill.

National's associate welfare spokesman, Chester Borrows, is looking at overseas approaches to the issue before drafting an amendment for his party's caucus to consider.

He said Britain used a similar mechanism to the New Zealand "reasonable force" defence, but "only in defence of cases of common assault, the lightest form of assault".

"There are also some provisions which exclude, for instance, application of force above the shoulders or that leaves a bruise or welt or breaks the skin or leaves a scar."

An Auckland University child psychology expert, Associate Professor Fred Seymour, said his preference was to stick with simply repealing section 59 because the authorities "will not be acting on the basis of smacks".

"Given their extraordinary workload [Child, Youth and Family] are hardly going to start responding in the extreme to children who are being smacked," he said.

"I also doubt people will be reporting people who give light smacks."

The Maxim Institute, a conservative Christian lobby group which supports National's intended amendment over the existing wording, wants the case law relating to reasonable force put into the statute, while retaining the flexibility to deal with these complex cases.

Legal counsel Nicki Taylor said the case law already "sets out the factors that juries should have regard to: for example the age and maturity of the child, the type and degree of force used, for example are there bruises, whether an instrument was used, the area of the body and the behaviour of the child".

She said a definition of reasonable force must allow complex individual circumstances to be considered.

Plunket Society president Kaye Crowther said the group wanted Section 59 repealed but would support a commentary that avoided parents being turned into criminals for lightly smacking or restraining their children from harm.