The 42-year-old shared the shot of her genetically blessed son, which was taken while they were on vacation.
'If you follow me on insta you’d know I rarely post photos of my son but I was going through our holiday photos and this one just stops me in my tracks every time. He melts my heart,' the doting mother wrote.
River is the older brother to his baby sister, Rosie, whom Megan gave birth to last September.
Megan and her fiance, Shaun Hampson, announced the arrival of their bub on Instagram.
'WHEN 3 BECOMES 4. Sweet little soul. You are already so blessed,' she wrote.
'Healthy as can be with a family that has fallen head over heels in love with you. A big brother that is already so attentive and protective, (who has also handled all these big changes like a boss ) a Dad who is so smitten with you and that you already have firmly wrapped around your little finger.
'And myself, who's been so lucky to have carried you in my belly for 9 months and to have had the pleasure and privilege of birthing you into this world (and can I just say .. we nailed it kid 👊🏼). I'm so committed to being the absolute best mother, friend and role model for you. Thank you for choosing me to be your Mama, my darling girl.'