I suggest the question is why you think that is an exceptionally wide confidence interval. I have seen such things many times with similar and larger samples.   Did you look at the variance on data within each replicate of the data? or within subpopulations?   I have no idea what the "nchild" variable represents but guessing that it may have something to do with children in families I might expect older respondents to have no children so including those families may increase the variability of the responses increasing confidence limits. Single male households are also less likely to have any children. ... View more