Mattias was born on 30 Dec., 2006. In 2018, Will told Parade that Mattias had begun exploring his old "Saturday Night Live" sketches. "It's fun when they discover," he told the magazine. Mattias also seems to enjoy sports, and in 2015, Will revealed that he and his wife had taken on the challenge of running their son's football team. "My wife and I are coaching, together, our 8-year-old's team," he told People at the time. "So, look out, AYSO Region 76. Here comes the Chargers!"