Your options for paying or receiving child maintaince
Child maintaince is payable - regardless of income. You can either have a private agreement, or go through the CSA. The CSA website contains lots of information, plus a calcuator, which can help you work out how much you may be expected to pay.
Many parents choose not to use the CSA, and have a private agreement, this link will explain further about private agreements, however, a private agreement is not usually legally binding or enforceable, unless it is written into your Separation Agreement.