"After they got married, they couldn't wait to grow their family," a source recently told PEOPLE. "Jack will be a great big brother. Katherine always says that he is the sweetest, most caring boy."
A friend also said: "They can't wait for Jack to have a sibling."
On Mother's Day, Schwarzenegger Pratt shared a heartfelt Instagram tribute to her own mom Maria Shriver, writing that the journalist and matriarch "made me want to be a mama."
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"Happy Mother’s Day to the greatest and most remarkable Mama in the entire world!" she captioned a photo of the mother of four throughout the past three decades. "We are the luckiest 4 kids in the entire world to have you as our mama. I am so beyond blessed to learn from you and you have made me want to be a mama for as long as I can remember."
"You mother not only us 4, but everyone you come in contact with," the mom-to-be added. "You are the Queen mother to all and I am so lucky to have you as my mom. I love you! ♥️."
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