The 45-year-old singer and 35-year-old actor came together for their 4-year-old twins, daughter Monroe and son Morrocan. Carey dressed as a witch, while Cannon, Monroe and Morrocan went as the Hulk, Batgirl and Batman, respectively.
Carey hosted a family-friendly celebration at a rented Beverly Hills mansion, where she partied with boyfriend James Packer later in the evening. The fête featured a dance floor, candy apple martinis and plenty of Sugar Factory candy.
"It was cool," Carey said of seeing her soon-to-be ex-husband to Entertainment Tonight. "It's really good for the kids. They decided on their own costumes -- they're superheroes. They've been celebrating Halloween since August."
Carey and Cannon married in April 2008, and welcomed Monroe and Morrocan in April 2011. The actor filed for divorce in December 2014 after several months of separation, and the pair previously reunited to spend Easter with the twins.