If I were you, I'd file for child support. At the end of the day, you're owed that money to help support your children. If he remains in prison for a longer time, then that's unfortunate for him but he has no valid excuse, other than pissing all over your generosity of not filing before given his mother's condition. Your ex-husband has a source of income, so he can pay at least some of what is owed, perhaps even all of it.