The proud mum, 28, uploaded the snap of her and Wayne Rooney's four-year-old boy, in his brand new school uniform.
KATIE PRICE SHARES BABY PHOTO OF PRINCESS
She captioned the picture: "Kai looking smart on his 1st day at school!!"
Earlier this week, Coleen shared her excitement for her son finally starting school, writing: "The time is nearly here… Kai starts reception this week!!! Big boy now!!"
Coleen, who is also mum to younger son Klay, recently launched her newest fashion collection for brand Littlewoods.
Of the collection, she said: "I love this collection. It's beautiful and feminine, designed to enhance and not hide curves.
"There's something here for every body shape, and the pieces can easily take you from late summer to autumn and beyond."
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Previously speaking of balancing being a mum and wife with her successful fashion range, Coleen said it's all down to Wayne and the children being supportive.
She told a British magazine: "I'm really lucky to have an amazing family who support me with the children, allowing me to work in the industry that I love, while being a hands-on mum, too."