Typically, a person’s sex is not shown on family charts — it is usually evident from their name. However, there are occasions where it is useful: a child who died very young and was never named, or someone with a given name that is traditionally associated with the opposite sex (for example, Philip and Nicholas have historically been used as female names).
To include the sex on charts and in report child listings, open the Main tab of the Current Person Other Detail dialog (click the … button next to the name fields) and check the appropriate option.