A child support parent's step-child can be considered to be their relevant dependent child if the child support parent has at least shared care of the step child and there is an order in force under section 66M of the Family Law Act in relation to the child support parent and the step-child.
The inclusion of a relevant dependent child means that a parent has an amount recognising their support of the child deducted from their child support income before calculating child support.
To obtain an order under section 66M FLA a person must be a “step parent” to the child, that is, they must:
A child support parent in a de facto relationship is unlikely to be able to obtain an order under section 66M in relation to the children of their current partner. For an order to be made under section 66M there must be proceedings between the child support parent and the child's parent about child maintenance (Mulvena and Mulvena and Butler and Edwards  FamCa 280).
If the child support parent is living with their spouse and step-child there may be no basis for the court to order that the step-parent pay child maintenance for the step-child (Unreported decision of Brewster FM  FMCAfam320 and an unreported decision of Family Court at Newcastle, per Mullane J,  FamCa 726).
If the child support parent and his or her spouse consent to an order it can only be made if notice has been provided to those who may be affected by it. The Family Law Rules, Division 4.2.4, Rule 4.16, require that the applicant serve a copy of the application, affidavit and financial statement on the step-child's other parent and any other person likely to be affected by the order sought. This would include CSA and any parent or carer of a child that the step-parent has a duty to maintain.
If a child support parent is providing financial support for a step-child and neither of the child's biological parents is able to provide financial support for the child due to death, ill health or caring responsibilities, the parent may have grounds for a change of assessment under the Child Support (Assessment) Act. See chapter 2.6.16 for more information.