Vach nacht
A vach nacht
or Brit Yitzchak is the night before the brit milah of a male Jewish child, when he is in need of added spiritual protection. A standard "vach nacht" custom, practised by many Ashkenazi Jews, is to have children come and recite the Shema Yisrael and other verses from the Torah near the baby. It is a pious custom to host a celebratory meal.
Origins
The Edut L'Yisrael brings sources for the custom to learn and post the night before the brit, as well as make a festive meal. He brings sources at length:Learning and prayer
Firstly, as stressed in the Kabbalistic sources, the night before the circumcision is considered a spiritually dangerous time for the baby; as such, the father would gather ten men to conduct a vigil to study Torah to protect him from metaphysical damage. Thus, this night is given the Yiddish name, "night of watching ".Secondly, non-Kabbalistic sources describe a practice several centuries old, that on the Friday night before the brit milah, a melamed would take his preschool-age students to say Shema near the baby, and afterwards receive candy.