Coleen and husband Wayne have enrolled Kai in a private school close to their home and he looks utterly adorable in his smart uniform.
With his black and yellow stripped blazer and matching cap, the four-year-old looks like he has come straight out of a Just William book.
Coleen took the picture of her boy before they headed off together and tweeted: "Kai looking smart on his 1st day at school!!"
On Sunday, she had also told her followers: "The time is nearly here..... Kai starts reception this week!!! Big boy now!!"
Kai has had a great summer with his mum and dad and has recently returned home from a sun-soaked holiday to Cyprus.
While footballer Wayne was back home in the UK working, Coleen, Kai and younger brother Klay were joined by grandparents Colette and Tony.
Despite only just starting school, Kai is already one well-travelled little boy. Prior to Cyprus, the Rooneys have already visited Dubai, Las Vegas, Portugal, Barbados and Brazil this year alone!
After receiving some flak from fans online about her jet-setting lifestyle, Coleen hit back: "Me and the kids love a holiday, haha!! #whynot #mylife."
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