How annoying the people that are there to help you, expect you to educate yourself..

Ok firstly are they collecting it for you or are you doing it privately?
If he misses payments or doesnt give them, he will be made to pay, alot of occaisions will be tax time.. I didnt think it mattered if they were in arrears your child is also of equal value, so that is abit strange..
It will effect your payments but for that amount i dont think a whole lot will go..You dont really get statements, you basically get an overview of what you should be getting and what you may expect to get in the coming future.
If he isnt earning money, i dont see how they expect him to pay? If i was you to cover your own behind, let the CS collect it for you, that way they are in control and can monitor payments, also when it comes to tax time, if you have been under paid from centrelink, they normally pay you the amount you should of got, so basically back pay you.. HTH