"You cracked my heart wide open," the mother of two wrote on Instagram about Malcolm Olivia ... Munn added, "He’s made me stronger and softer in ways I never knew I could be. Happiest Birthday ...
Munn shares her two kids — Méi and Malcolm — with husband John Mulaney Olivia Munn/Instagram Olivia ... and smiling as Munn says, "Happy birthday! Hi, happy birthday! Happy 4 months!" ...