I've heard that some men fast on erev Pesach for their firstborn son until that son old enough to fast for himself. Is that halakha? Where does this come from?
The Leviim wash the hands of the Kohanim when they go up to bless the people. If a Levi is not available a first born (to the mother) can wash (according to the Askenazi custom) instead, Orach Chaim ...