Jaden, 14 and 15-year-old Kylie have been friends for years, but became romantic recently, reported Us magazine.
The young stars were most recently spotted together on a lunch date at Caffe Nero in London's famous Piccadilly Square, when Jaden was in town to celebrate his friend Justin Bieber's 19th birthday.
Kylie, daughter of Olympian Bruce Jenner and businesswoman Kris Jenner, was previously linked to Australian pop star Cody Simpson.
She denied the rumours, saying, "Cody and I are just good friends.