把小的送回国? Does he agree with it?

When he pay child support, he has the right to visit his son, he has the right to stop you sending the child to China, he has the right to take the kids away from you.
And if you try to punnish him more for the money, don't forget, you are making your children's father having a bad life. And your kids will have a bad days when they stay with him.
And after you find a job later, he can go to court to modify the child support. And if he get marry again, has another child, he can reduce the child support again.