A child left out of the will could potentially succeed in a claim for maintenance and support under the Family Protection Act.
These claims are all considered separately on their own facts, but the main question is whether or not the deceased had a moral duty to leave something in his/her will to the claimant. The answer to this question is usually determined with reference to factors such as any other competing moral claims, the financial position of the claimant etc.
The view that is most commonly taken by the courts in New Zealand is that parents always have a moral duty to leave something to their biological children in their estate. Bearing this in mind, it is very likely that your child will have a successful Family Protection Act claim on your estate if you decide not to include him/her in your will.
If you would like further advice regarding potential claims on your estate, please make an appointment with Scott Donaldson or Malcolm McKenzie.