Max Nixon-Marinoni was born on Feb. 7, 2011. He is the son of Nixon and her wife, Christine Marinoni. Marinoni gave birth to Max, and in a 2019 Instagram post, Nixon appeared to reveal the identity of Max's father: she captioned a photo of Max in a partially finished Halloween costume with "When your dad's a costumer and you always wanted to be Pennywise..."
The costumer in question is in the photo with Max, working on his costume — he's Michael Growler, a costume designer who worked with Nixon on the play Rabbit Hole and on the Sex and the City films. On Father's Day in 2018, she shared a picture of her, Max, and Marinoni, with Growler and his husband, William Bowers, captioned "To all of the amazing dads in our children's lives: Happy #FathersDay!"