The 35-year-old star channeled her inner child, sans kids, wearing white sweats, a matching sweatshirt with a female resembling herself on the sleeve, and pink Minnie Mouse ears.
31-year-old MGK played along, also sporting Mickey Mouse Ears.
The duo held hands as they made their way through the park at Disneyland on Thursday.
Fox and her rocker boyfriend weren't trying to hide from the paparazzi either, especially MGK who wore a bright blue sweat outfit.
The hottest couple in Hollywood seemed to enjoy their day out at the adventure park, riding rides like Thunder Mountain Railroad Roller Coaster, Millennium Falcon, and the Rise Of The Resistance located in Star Wars: Galaxy's Edge.
Fox and MGK didn't spend the day alone. The Transformer star's parents -- mom Gloria and dad Franklin -- were photographed walking alongside the happy couple of one year.
It's an interesting move that Megan didn't bring her three sons along, especially since her estranged husband has been parading his time with them around social media lately.
As Radar reported, Brian Austin Green collected major kudos from fans when he shared a post showing his girlfriend Sharna Burgess swimming with his and Fox's kids over the weekend.
She seemed to fit into the stepmom role perfectly while posing in the water with Journey, 4, Bodhi, 7, and Noah, 8.
Their fun with the kids didn't stop there. The Beverly Hills, 90210 actor was photographed taking his sons and girlfriend to the movies, followed by a Target run, where one of the boys was seen holding Sharna's hand.
Meanwhile, fans couldn't help but notice Fox seemed to be getting up to no good with MGK over the weekend.
She jumped on the stage during his Indianapolis performance and lit up a cigarette. Days later, the two had a run-in with police.
Fox has scolded her soon-to-be ex-husband in the past, accusing him of "using" the boys on social media to make her look like a bad mom, but going to Disneyland without your sons, won't score you brownie points, Megan.