Is it permissible to work in stores that sell women's, men's, and children's clothing in America, knowing that they are not designated for Muslims and sell ordinary clothes to the American people?

If these clothes are permissible to wear, then there is no harm in selling them. However, if they are inherently forbidden, or if they were originally permissible but it is highly probable that they will be worn in a forbidden manner, such as clothes for ostentatious display (tabarruj), then it is not permissible to sell them, whether to Muslims or non-Muslims.