"Best thing ever," Kourtney Kardashian's ex captioned an Instagram video Sunday

By Michele Corriston
Updated August 10, 2015 08:45 AM
Courtesy Kourtney Kardashian

It doesn’t get cooler than this.

Scott Disick is spending time with his kids after splitting from longtime love Kourtney Kardashian in July, and he let them have a jam session in a Mercedes.

“Best thing ever,” the dad of three captioned an Instagram video Sunday of son Mason, 5, and daughter Penelope, 3, dancing to Demi Lovato‘s hit “Cool for the Summer” inside his car.

There’s no sign of baby boy Reign, 7 months, but Kardashian, 36, spent the weekend celebrating her little sister Kylie Jenner‘s 18th birthday.

Disick, 32, seemed to suggest that he regrets the breakup earlier this month, posting an Instagram of his solo place card at a wedding with the caption “When you realize the grass isn’t always greener.”

The reality stars ended their relationship after Disick was photographed partying on vacation, and he kissed an unidentified woman in Las Vegas weeks later.

“He really screwed up, again, and the entire family knows all about it,” a source told PEOPLE.