Kieran has two children with the glamour model - Jett, two, and 22-month-old Bunny - and wants to officially become 14-year-old Harvey's dad but fans hit out claiming it was unfair as her former husband Peter Andre had been a fantastic dad to the youngster during their marriage.
Katie wrote on Instagram: ''Pete doesn't want to adopt harvey and doesn't see him anymore and doesn't ask to see him anymore so don't judge on something you don't know about and kieran is ana Omg with the children and even pete will say that (sic).''
Kieran told Britain's OK! magazine: ''I've always thought it would be good because I'd like us all to be connected. He is my child at the end of the day. Why not actually make him mine, because he feels like he's mine anyway? He's my stepson no matter what happens.''
Katie - who also has children, Junior, 11, and Princess, eight, with Peter - praised Kieran as a ''great dad'' and also slammed Harvey's biological dad Dwight Yorke.
The former footballer split with Katie, 38, while she was expecting Harvey and has not had much to do with his son, suffers from Prader-Willi syndrome, autism and ADHD.
She said: ''I've sent him pictures of Harvey but I never get anything back. Anyone can fill a pram, but it takes a real man to be a father. I think he's an absolute fool and it's a shame Harvey hasn't had the support he deserves from him.''
While she was married to Peter, he also spoke of his desire to adopt Harvey but claimed it had been prevented.
He said: ''Unfortunately, I'm not allowed to adopt him and it's not going to be an easy road. I love him.''
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