filial

Filial is descended from Latin filius, meaning "son," and filia, meaning "daughter," and in English (where it has been used since at least the 14th century) it has always applied to both sexes. The word has long carried the dutiful sense "owed to a parent by a child," as found in such phrases as "filial respect" and "filial piety." These days it can also be used more generally for any emotion or behavior of a child to a parent. You might suspect that filia is also the source of the word filly, meaning "a young female horse" or "a young girl," but it isn't. Rather, filly is from Old Norse fylja.