Star Wars is continuing to suggest Darth Vader kidnapped Force-sensitive children across the Empire - but it's currently not clear why. Star Wars: Episode III - Revenge of the Sith ended with Palpatine successfully establishing the Empire, and it marked the beginning of the Dark Times. In those early days, the idea of rebellion was just a distant dream, and the might of the Empire terrified any who would oppose it.
In late 2019, Lucasfilm published George Mann's Star Wars: Myths & Fables, a book that collects in-universe legends that are all said to contain a fragment of truth. One of these, "The Dark Wraith," suggested Darth Vader spent considerable time hunting children across the galaxy. This was presumably an extension of Darth Vader's mission to find Force-sensitives, but previously he'd been thought to kill everyone he discovered. The legend is sourced from a lesser-developed planet, suggesting Vader was attempting to avoid attracting too much attention with this mysterious mission.
Lucasfilm has just published a sequel to Myths & Fables, called Star Wars: Dark Legends, also by George Mann. It contains another tale, "The Orphanage," which recounts a similar myth - this time one sourced from an orphanage on the planet Gaaten. This orphanage looked after children who had lost their parents during the Clone Wars, and it seems it was periodically visited by members of Vader's Inquisitors. Again, it is interesting to note how surreptitious the Inquisitor was, because he only ever came at night - and took just one child at a time, so as not to draw suspicion. An Order 66 survivor called Kira Vantala found herself drawn to Gaaten regardless, and managed to rescue one child from Second Sister's clutches.
This indicates the scale of Darth Vader's mystery mission was far greater than had previously been suspected. Not only was Darth Vader himself kidnapping Force-sensitive children, the Inquisitors were also involved. It's unlikely Darth Vader was using Imperial resources like this without the Emperor's blessing, meaning this was presumably one of Palpatine's own plans. But it's difficult to say what the Emperor's agenda was; it doesn't appear to have been an extension of the Inquisitors, because they had all been killed by the time of Luke Skywalker. None of these Force-sensitive children have ever been seen again.
These are only legends, but Lucasfilm has stressed that they contain a seed of truth. Given that's the case, readers are getting a fresh glimpse of Darth Vader's activities in the Dark Times, although it only serves to deepen the mystery of why he's kidnapping the Force-sensitive children. Hopefully it won't be long before Star Wars provides some more concrete information.