Hello Jingyi,
The file A_INDALL includes basic biographical info about all individuals in the households, that is, their age, sex, etc and identifiers of mothers, fathers.
The file A_NATCHILD includes biographical information about resident and non-resident children of any household member who gave a full interview (A_IVFIO=1) and gave valid answers to the questions about their resident and non-resident children (A_LCHLV etc)
Using the method that Gundi outlined in #755 you can get
1. information about the sex of co-resident children from INDALL
2. You can also find information about the sex of co-resident children from A_NATCHILD but only for individuals who gave a full interview and valid responses
3. You can find information about the sex of non-resident children from A_NATCHILD but only for individuals who gave a full interview and valid responses
However, as you can see it is not possible to get information about non-resident children of adults (16+) who were not interviewed (N=11,704) or who were interviewed and reported having at least one child (a_nnatch>0 or a_lnprnt>0) but did not answer questions about their children (N=1910).
Does this answer your question? If not, please do not hesitate to ask us again.
Alita