The 34-year-old fitness and wellness expert already has daughter Carmen, five, and sons Rafael, three, Leonardo, 22 months, and Romeo, 10 weeks, with her husband and actor Alec, but has said a fifth might be on the cards in the future as her daughter wants a younger sister.
She said: ''I have a daughter and then I have three boys. And my daughter is very sure that she is going to have a sister.''
Carmen already has a big sister in Ireland Baldwin, Alec's 22-year-old daughter from his previous relationship with Kim Basinger, but is determined to have a younger one too.
Hilaria added: ''She does have a sister - she has Ireland, and Ireland is so wonderful and they have a great relationship. But there's something about a little sister that she really wants.''
And when asked if 'Boss Baby' star Alec, 60, is on board with the idea of another child, Hilaria thinks it's ''very possible''.
Speaking on the 'Today' show, she said: ''I think it's possible. Not [for sure]. Alec thinks it's very possible. He comes from a big family.''
This isn't the first time Hilaria has spoken of her daughter's dream to have a little sister to join her three younger brothers, as the beauty previously said Carmen as ''disappointed'' when newest addition Romeo was born.
Hilaria said: ''She was a little bit disappointed. [She said,] 'How about you have a girl first, then you can have another boy?' I was like, 'It doesn't work that way! I don't get to choose.'
''She's like, 'No, you don't understand, Mommy. It's going to be a girl.' I was like, 'No, I promise. I promise you it's a boy.' She is committed to a fifth child.''
Meanwhile, Alec previously joked that his spouse would have to find another husband if the pair are to try for a fifth baby.
He said: ''My daughter Carmen said, 'You have to have another one. We have to have another girl so we have another girl in the house. And my wife says to me, 'I want to have maybe one more, Alec. We have one girl.' And I said, 'I hope you and your next husband are very happy together.'''