Credit: Flynet;

No cat fights here!

Ashlee Simpson and Pete Wentz split up in February, but they appear to be happy to put their differences aside for the sake of their son Bronx. On Monday, Wentz, 32, Ashlee, 27, were joined by the Simpson family -- including a pregnant, makeup-free Jessica! -- to celebrate Bronx's third birthday at The Coop in Studio City, Calif. 

Ashlee and Bronx had matching kitten whiskers painted on their faces, while Jessica, 31, opted for a natural look. The designer's fiance, Eric Johnson, and parents Tina and Joe Simpson were also on hand for the fete. 

Although she's amicable with Wentz, Ashlee has a new man in her life: Boardwalk Empire's Vincent Piazza. Ashlee and Piazza have been dating since June, and in September, the actor introduced Ashlee to his parents.

Fortunately, Piazza and Wentz haven't had any issues with one another. "It's been really great. So there is no head butting," Piazza joked to Us Weekly in September about his relationship with Ashlee's ex. "You'd see the marks if there were!"