"Mom, dad and big brother Sid are doing great!" the rep said.
Mollen already shares 3-year-old son Sid with Biggs. She shared photos on Instagram after news of Lazlo's birth broke, including a picture of herself with Biggs and her doctor at the hospital.
"This man claims he doesn't know anything about Instagram and yet every time I talk to him, he knows exactly what is happening on my Instagram. #DrSassoon4Life #RideorDie #AlbertSassoonattack," she wrote.
"In this pic we were still calling him Sid 2. #babybiggs," she captioned the sweet photo.
Biggs and Mollen married in Los Angeles, Calif., in April 2008. The actor said in an interview with People in 2014 that parenthood "completely changed" him and Mollen.
"She sees it in me, and I see it in her, and we're stronger now because of it," he said. "The change that happens is so tangible. It happens overnight, and it's the craziest thing."