There is a principle that government contributions should not replace financial support from parents. To be entitled to claim Family Tax Benefit Part A for a child, a person must be caring for the child for at least 35% of the time. Family Tax Benefit Part A is affected by the amount of income a family receives and the amount of Child Support that is received for each child.
Your Family Tax Benefit Part A may be worked out using a different amount than the Child Support amount in your private agreement. Where a Child Support Agreement is in place, Family Tax Benefit will be paid on the basis of the Child Support that would have been payable if the agreement had not been made (the notional assessment). This can be an issue with Binding Child Support Agreements where the amount payable is less than the amount calculated by the Child Support Agency