Demi Lovato joined We The Kings at Elysian Park in Los Angeles a couple of weeks ago to film the music video for WTK's newest single, "We'll Be A Dream."

The video features an impromptu "childhood battle" -- with weapons that included pillows, water balloons, ketchup, and chocolate syrup -- and Demi performing with WTK.

It's a huge song for We The Kings -- besides being a duet with Demi, singer Travis Clark tells J-14 that it's his fave track off WTK's album Smile Kid. "It's a song all about growing up and wondering what you're going to be," he says. "That's a really emotional song for me because it all came true."