Writing in Now magazine, said: "I'm nearly at my pre-pregnancy weight but I want to tone up."
Last month, the former glamour model posted Selfies in her undies on social media site You Gossip, displaying a concave stomach.
But she said she is taking her post-baby fitness regime 'slow and steady' – under the supervision of Bunny's dad Kieran Hayler.
The 36-year-old wrote: "I'm taking it slow and steady – walking on the treadmill and light cardio, plus some weights – and Kieran will have me on a stricter eating plan."
She also had some advice for the Duchess of Cambridge, who recently announced that she and Prince William are expecting their second child.
Katie wrote: "I want to wish them good luck in having two little ones under the age of two.
"The biggest challenge is getting used to the tiredness again when you've got sleep back to normal – it will all change."
Katie is such a fan of the Royals that Kate's name was even on her short list of baby names.
Katie told OK!: "We really struggled to decide on a name. I wanted to call her Duchess Kate or just Duchess, but Kieran didn't like that, so we've chosen Bunny, which we both like."
She added that Lady, Disney, Bambi, Ethel and Peggy were also on her baby names shortlist. Katie already has a daughter called Princess Tiaamii with former husband Peter Andre, as well as sons Harvey, Junior and Jett.