[header] How to collect unpaid child support [title] Talk to the other parent. [step] If you are on speaking terms with the other parent, you may be able to work things out on your own and make arrangements without involving the courts. [substeps] This is especially true if you know the other parent has encountered a temporary hardship but will soon be able to resume regular payments again. 
If you do come to an agreement with the other parent regarding back child support, make sure you get that agreement in writing. You also may be able to file the agreement with the court or get a judge to approve it so the agreement itself is legally enforceable.