The 43-year-old actress and 39-year-old singer reunited to celebrate the occasion at Disneyland. The former couple are the parents of Apple, who turned 12 on Saturday, and Moses, who turned 10 in April.
"When your parents can't handle #thundermountain anymore so they wait for you at the bottom. #disneyland #thehappiestplaceonearth #birthdayweekend," Paltrow captioned a photo of herself with Martin.
The Mortdecai actress had dedicated another post to her daughter on Saturday, calling her the "great love" of her life. Apple celebrated her birthday with friends earlier in the day, at a birthday brunch that included Blue Ivy, the daughter of Beyoncé and Jay Z.
Paltrow and Martin remain friendly after finalizing their divorce in April. The pair were married over 10 years before announcing they were "conscious[ly] uncoupling," or separating, in 2014.
"It's like we are still a family, but not a couple," the actress explained of their post-split dynamic in the May issue of Marie Claire Australia. "I think we are better as friends than we were [married]. We are very close and supportive of one another."
"It hasn't always been easy for us because you have good days and bad days as you do in life with anything," she admitted. "But I feel lucky because Chris has been willing to push himself for the sake of the kids and help me co-create this new family."
Paltrow will next star in TV movie One Hit Wonders and is also slated for 33 dias with Antonio Banderas. Martin last released A Head Full of Dreams with Coldplay in December and kicked off an accompanying tour in March.