Sharing the most adorable picture of the three-year-old posing in their home's hallway, Storm wrote: "Excited for his first day of nursery at his new school #wheredoesthetimego #uniformandeverything #bigboy #myboy #cooperkeating #cutie #myheartcouldburst #proudmum."
In the cute snap, Cooper can be seen wearing his uniform, a green tracksuit bottoms and a white and purple polo top, as well as matching blue and green trainers.
Cooper, three, posing ahead of his first day at nursery
Friends and fans of the family found the picture endearing, with singer Natalie Imbruglia commenting: "Such a cutie."
Storm's friend, who is Cooper's godmother, wrote in disbelief: "That is not my godson. I saw him two weeks ago and he was still a little lad. I'm sorry, but I think you have the wrong kid."
Whilst proud step sister Missy, added: "Wow the cutest… the Jordan's thoooo #coolestkid."
One fan couldn't help but comment on how grown-up he looks, adding: "Gosh he's had a massive growth spurt!"
Another remarked: "Oh my goodness... not a baby anymore!"
The couple's fans couldn't believe how much their eldest son had grown
Cooper's milestone comes a couple of weeks after the family returned from the most idyllic holiday in Turkey.
During their stay there, both Storm and Ronan shared envy-inducing pics whilst staying at Ciragan Palace Kempinski, which is an Ottoman Imperial Palace and Hotel overlooking the Bosphorus strait.
After relaxing in Istanbul for a few days, they continued their holiday in Turkey by travelling to Bodrum where they enjoyed a beach break with their two children Cooper and Coco, as well as Ronan's son Jack.
"The most amazing day sailing the sea on the #CobraKing in beautiful #Turkey ??. Thank you @mine_kalpakcioglu for putting us in touch with the best in this land... the @cobrayacht team were so brilliant, as are the staff at our stunning villa in @barbarosreservebodrum #DreamHoliday #LoveThisPlace," Storm wrote on Instagram next to several photos of the family's day at sea.