A proverb meaning it's good (or lucky) to have a girl first and then a boy (i.e., a daughter followed by a son).
祖父は子どもの順番について『一姫二太郎がいい』と言っていた。
My grandfather used to say that having a daughter first and then a son is best.
昔は一姫二太郎という考え方が一般的だったが、今はあまり気にしない人も多い。
In the past the idea of 'a girl first, then a boy' was common, but nowadays many people don't care.
友人夫妻は一姫二太郎の順で子どもを授かった。
My friends were blessed with children in the order of daughter first, then a son.
Colloquially, it can be used to mean one girl and two boys are ideal (a more recent casual usage).
彼は『家族は一姫二太郎が理想だ』と冗談めかして話した。
He jokingly said that his ideal family would be one daughter and two sons.
最近は性別にこだわらない人も増え、一姫二太郎という考え方は減ってきた。
Recently more people don't care about gender, and the 'one daughter two sons' idea has declined.