Ok , maybe I am a little to close to this situation , as I have dealt with and am still dealing with a very similar situation. Lets get to it, I would not tell her about his "illness". You have no way of knowing whether or not that is true. And since he has the obligation, why can't he speak with child support on him own behalf? My children's father, who is not active in their lives, nor does he pay the court ordered support, and has a huge arrearage, did the same thing , only I found out that he was lying about the "illness". Since I didn't contact child support , he did, and basically , they told him that they have all sorts of job training and resources to help them find jobs if they don't have one, so the support still needs to be paid. I am not sure about this case, I don't know your ex, but I would let him deal with that. If he indeed does have this illness, then he needs to take the initiative, and contact child support so that he know what steps he needs to make in order to pay it. If it is arrears, then it is an order that was not paid; i don' t think they can ammend an order that was not only already established, before his illness, but was not paid to satisfaction , before his illness, and before the child turned 18. It is a shame, because we should not have to do it alone, so I think you should let it play out. I know you have done it alone all of these years, but who couldn't use some extra money? Look at it that way. It could go towards college or a vehicle. My point is , if they are going to pursue it, why not take it. If this illness was just realized, what does that have to do with before, when the child was younger than 18? That was not a factor, then, so if he is only paying arrears, I see no need for that to even be considered. I know that this may sound a bit cold, but you need to think realistically. My thing is, if the fathers were present , there would be no need for child support, so take it if it is given.