Duff, 30, gave birth to her first child, a baby girl, on Monday after being induced over the weekend, Us Weekly reports. She and Rosenberg named their daughter Ryan.
Though Haylie missed celebrating Mother's Day by one day, she tweeted a message of solidarity with her new mom friends on Sunday.
So proud of so many of my "new mom" girlfriends too! Hard but rewarding work! Happy to be doing it with yall! 💖— Haylie Duff (@HaylieDuff) May 10, 2015
Duff's younger sister, Hilary, hosted a baby shower for Haylie back in March, with guests including Lauren Conrad and Jenna Dewan Tatum, according to Us.
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