First order of business: figure out all the villainous characters in the first book who can come to the forefront in sequels.
The nature of the plot requires several. And I carefully tied off the major villains, on account of the way the main characters were not idiots and knew perfectly well that villains who are not disposed of very finally tend to come back -- when the baby's born is most popular, but they never stop. (None of the witches -- or wizards, either -- were burned. It was final nonetheless.)
But there were more minor ones, who could escape. And grow more powerful.
The chief one is one mentioned in the backstory. But there will be more about the edges. And even before I thought of the sequels, one character had cautioned another in the first story that there would always be witches and curses and other threats, she could not put her life on hold until she was safe. There will be more.