From GameWatcher: “Little Nightmares 2 has been officially announced during the first day of this year’s Gamescom festivities, but the focus on two-character gameplay made us think that Tarsier Studios has cooperative gameplay in mind this time around.
Developers have now confirmed that the second main character, Six, will remain an AI-controlled character, even though she will have way more agency than ever before. Sadly, this means no COOP whatsoever.”
Source: N4G PC Tarsier Studios confirms that Little Nightmares 2 "won't have co-op support"