"They call me 'Mom,'" Holmes told Parade, referring to Cruise and Kidman's children -- Isabella, 15, and Connor, 13.
An insider told Us Weekly, "Isabella especially took to (Katie) right away."
The magazine noted that Holmes' statement seems to coincide with Kidman's revelation on British television that her two kids no longer "call me Mummy."
"It's Mum or sometimes Nicole. I'm like, 'Hey!'" Kidman said.
However, Kidman's representative told Us Weekly she was "joking around" when she made the comment.
Said to be further contributing to tension in the family is how Cruise is raising the children as Scientologists, something Kidman is "not cool with," a source told Us Weekly.
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