The retired glamour model claims her former spouse is taking their children Junior, eight, and Princess Tiaamii, six, away from her for the whole of Christmas.
In a series of messages posted on Twitter, she wrote: ''What kind of Dad doesn't let their children see their mum not even 1day over christmas when the children want 2 c their mum #fakefamilyman.
''Did you know he loves his kids. This shows how much he loves his kids. (sic)''
Katie also has four-month-old son Jett Riviera with her new husband, Kieron Hayler, and 11-year-old Harvey from an earlier relationship - whom Peter raised as his own while they were married between 2005 and 2009 - but she claims he is now neglecting his fatherly duties.
She added: ''Can someone remind him he has a son called Harvey that calls him dad or was that just for show too
''I wouldn't do this to pete and deprive him and his newborn from seeing the kids for its 1st christmas. (sic)''
Peter, 40, and Katie, 35, are currently locked in a legal battle and relations between them are at an all time low.
In previous years they have split the festive season so they both had time with their children, with one taking them for Christmas Eve and Christmas Day morning, then dropping them with the other for Christmas Day evening and Boxing Day.
Peter - who is spending Christmas with his pregnant fiancee, Emily Macdonagh and her family - has yet to comment on Katie's allegations.
The former couple face a High Court court battle next March after Katie accused Peter of leaking details of her private life to the press.