Off the top of my head, for what it's worth, I have seen instances of group baptisms of a "backlog" of children in North America in Fairfield Co., CT in 1700s, in New London Co., CT in 1700s, in Queens Co., NY in 1700s, and in Albany Co., NY in the 1800s. In the last case, it was indeed just after the children's mother had died. The circumstances of the other sets of baptisms are not as clear.