Games Workshop's Warhammer settings have been adapted into novels since the late 1980s, but never anything quite like the two books they've just announced. The Warhammer Adventures line is, as their website puts it, "perfect for bookworms aged 8-12 who want to read about heroes, aliens and monsters."
Of the two stories announced so far, Attack of the Necron is a Warhammer 40,000 story while City of the Lifestone takes place in the Age of Sigmar setting. Young adult fiction doesn't shy away from mature themes, but it's still tough to imagine the Warhammer 40,000 universe—the setting that gaves us the phrase "grimdark"—being the basis for kid's books.
On the other hand, Games Workshop fans are an aging audience, many with kids of their own, and a way for them to pass their love of chainswords and big shoulderpads down to the next generation could be a welcome thing.
Over on Facebook, Black Library (who publish the Warhammer books) have been fielding complaints and queries from fans worried their beloved Warhammer is going to be watered-down. "We havn't [sic] watered down anything - we just added a shallow end", they've said. And: "It's still the grim darkness of the far future, but there's a night light on."
Before anyone gets too concerned about Warhammer being changed, it's worth having a look at author Stephen Baxter's excellent article about the early days of Games Workshop's original novel line. Even the books that weren't for kids have always had content guidelines, and as Baxter puts it, "We had to imagine our ideal reader as 'an intelligent 18-year-old', we should avoid sadism and explicit sex, and 'the keynote above all should be fantastic adventure'."