When submitting my data extracts it seems like we can only attach sex and race characteristics for the mother and father.
If you are interested in the sex and race of a person who is within a household, you will just need to include SEX and the appropriate race (i.e. RACE) variable in your extract. In the rectangular data format (the default), where data is available, all household respondents, including children, will have one row of data in the sample (i.e. age, sex, race, education, etc.). Attaching a characteristic, such as sex or race of mother/father puts the mother/father race/sex in the same row as the child’s observation.
However, it sounds like you may be attempting to attach a child’s sex/race information to a parent observation. Unfortunately, this functionality is not provided with the attach characteristics option since there can be any number of children associated with a parent. You can, however, attach this information yourself using your extract. We have some sample syntax, that may help get you started, available here.