Well, you have more than one child and those children can have more than one child each because you don’t live in China and don’t have the restrictions. It is not fair to expect what you’d have in China if you’ve relocated to the US and now live an American lifestyle with more costs, bigger homes, different living arrangements. Or at least you shouldn’t expect your children to pay you just because it is tradition. You’ve raised American kids.
I knew a guy who married a woman and it was her family’s ‘custom’ to support their mother. When they got divorced, the court didn’t consider this payment to the mother as a necessary expense and if the ex-wife wanted to continue it, it had to come out of her monthly support. That’s the American way.