Hudson, 36, and Jonas, 23, sparked rumors of a new romance when they were spotted having a magical day at Disney World together in late September.
"It was just a fling," a source close to Hudson tells PEOPLE. "It's definitely not anything serious."
"They are both single and seeing other people too. Kate's mostly focusing on her boys and doesn't want a serious relationship right now."
Neither reps for Hudson or Jonas would comment when contacted by PEOPLE.
The mother-of-two has been single since calling off her engagement from Muse frontman Matt Bellamy in Dec. 2014, while the Scream Queens star split from Olivia Culpo in June after two years.
"I'm definitely dating and hanging out," Jonas told PEOPLE at the LA premiere of the second season of his DirectTV show Kingdom on Tuesday. "I am single, but I'm hanging out with people and just getting to know people and enjoying seeing what's out there."
And Hudson has been keeping busy, not only raising her sons Ryder, 11, and Bingham, 4, but also focusing on her fitness. Recently, she showed off her impressive abs to tease her upcoming Fabletics collection.