You can not file I-824 to do the following-to-join for your kids' GC application because you are the immidiate relative/spouse of a US citizen and thus, your kids can not be your derivative status.
If your two child are less than 18 years old, your hu*****and needs to file additional two separate I-130s now for your two kids, respectively. Then, after the I-130s are approved, your kids can apply for the immigration visa in China. The wole process may take 6 months to one year.
Another choice is that your two kids get the b2 visa to enter US and then, your hu*****and can sponsor them GC application as he does for you. But It is probably difficult to get the B2 visa.
