Speaking to the Australian edition of Harper's Bazaar magazine the star revealed that her eldest daughter Sunday Rose, three, calls herself 'mummy's little cub'.
New baby Faith, born by a surrogate, is also said to be a 'calm baby', and she told how great it is to be a new mum at 43.
Nicole also said that her husband Keith Urban calls her a 'raw egg' because she is so sensitive.
She said, 'Sunday says, 'I'm your little cub', and isn't that a nice description, because I do feel like a lioness and I'd do anything to protect her.'
She added, 'It's also great to be a mother again at 43 because I can have the lifestyle where I can work for a bit and then take eight months off, and most working mothers don't get that.'