Taking to his Instagram Stories, the chef posted a picture of River smiling broadly whilst wearing a pyjama set from Jool's Little Bird collection which is available through Next.
WATCH: Jamie Oliver dances in car with youngest son River in adorable video
"Happy indeed @joolsoliver," the proud dad wrote. Jools was quick to regram the picture to her own account and added "My baby" together with a pink heart emoji.
Jamie and Jools welcomed their youngest child, River Rocket, in August 2016. They are also parents to daughters Poppy, 19, Daisy Boo, 17, Petal Blossom, 12, and son Buddy Bear, 10.
Asked how she thought he would get on by Zoe Hardman, host of the Made By Mammas podcast, Jools revealed: "I don't know. He's a funny little boy. I don't know, I really don't know. He really loves girls, he doesn't really like boys, as in playing with boys, and he's going to an all-boys school which is a bit worrying."
Jamie and Jools shared the most adorable picture
She added: "And he loves dressing up, he wears a dress every day, I'm not revealing anything, I just think he is the most different… I've never met a child like him. So he is theatrical, interesting, totally like a little girl, and it's so funny because he and Buddy get on really well but Buddy is a real boy and he is like a little girl, but a boy so I don't know. I have no idea. I just hope they have Frozen dresses in the dress up box, in an all-boys school. He is just a character."
Sharing her nerves with both Zoe and co-host Georgia Dayton, she continued: "He is quite OK to leave me, and he is good with other people so we'll just see. I just don't know, it could go either way and I'm thinking: 'I am so worried,' I just really want him to enjoy it so I can relax.'"