What are you confused about? It sounds like you need to file 4 years worth of tax returns. You would probably be expecting a refund, because if the IRS thought you owed them they would be sending you nasty letters. No, if you’re behind on child support, then it is possible that your refund will be taken for that debt, but that’s a stupid reason not to file. Because even if your refund is taken for a child support debt, it will reduce your debt for the future, and you haven’t seen any of that money anyway because you haven’t filed. And if you do owe a tax payment, the penalties and interest are quite substantial at this point and only growing larger.