Katy Perry's gotta get some practice! As Orlando Bloom's fiancee, she'll soon be in charge of co-parenting his son Flynn, along with the boy's mom Miranda Kerr (who's got another child with new hubby Evan Spiegel of Snapchat fame and a second one on the way!).

The trio dined at Nobu Malibu Saturday night -- and boy was that place busy! Mariah Carey was there with ex Nick Cannon and their twins Moroccan and Monroe and Sofia Richie enjoyed the seaside hotspot's famous sushi with her brother Miles, her mom and some friends, celebrating a pal's birthday. Talk about an A-list night!

Meanwhile, we happened to spot Katy's ex-husband Russell Brand at LAX with her adorable daughter Mabel -- first time we've seen her! The funnyman and his adorable girl made their way through the terminal to a waiting car.