Ex-Wife is Cold-Hearted

I'm married to a wonderful man, and we just recently had a beautiful baby boy in August, I'm pissed off, because all of a sudden out of nowhere he's ex wife decided that she needed child support for their two children, now I'm not trying to sound mean about his children, but they are the most ungrateful kids I've known in my life, he has tried everyday the whole time we were together to try and talk to them and find out what they need and all that, he sent his son a birthday card and the kid has yet to say thank you, I'm more upset at the fact that his ex-wife waiting until he had a new baby to decide she wants him to pay child support, I love him very much and he is a great father, I watch him with our baby boy and you can tell he misses his children, they moved to a different country when they were babies, becauase their mom left him with nothing. I dont like to see him like this he makes money but with the bills getting high and having a newborn in the house, sometimes we have to stretch what we do have left, which sometimes is not much. I cant believe how cold-hearted his ex wife is, it's like she dont care that he just had a new baby and the older kids dont care about him, expect when it comes to money and I dont think that's fair to pay for children that would rather watch you die than claim you as their father, when you've done everything in you power to talk to them and keep in contact, I dont know what to do or even what to tell him, other than I'm right here and I'm not going anywhere.