The 47-year-old singer shared posts Sunday on Snapchat from her outing with Shelton, 11-year-old Kingston, 8-year-old Zuma and another friend, including a photo of Shelton sitting in the boat and a clip of Zuma catching a small fish.
"I can see him!" Stefani can be heard saying as her son reels in the fish, with Shelton encouraging, "Catch that sucker!"
Stefani shares Kingston, Zuma and 3-year-old son Apollo with ex-husband Gavin Rossdale, from whom she split in 2015 after nearly 13 years of marriage. She discussed her approach to parenting in an interview with People this month.
"I was in a band and free my whole life, so I always thought I would be really free with [my kids] and do whatever I wanted, like, 'Oh, I'll take them out of school,'" Stefani told the magazine. "But you learn that when they have boundaries is when they feel the safest."
"The hardest thing to do is having a discipline chat and follow up on all those things," she confessed. "It's work, you know? But that's where you get the results."
"I see a constant fear of 'How am I gonna make sure these kids are good people?'" the star said. "I love when they still play and you're like, 'Oh good. They're still doing that.'"
Stefani and Shelton confirmed their relationship in November 2015 following their respective splits from Rossdale and Miranda Lambert. Lambert is now dating Anderson East, and discussed the singer in the August issue of Cosmopolitan.