"He's brought a lot of joy to the family," Margulies' father, Paul, told Usmagazine.com about the birth of baby Kieran.
Margulies and Lieberthal married in November.
"He has some of Keith's features and some of Julianna's features," Paul Margulies noted, "and they're changing every day."
Margulies is best-known for her roles on the TV shows "ER" and "The Sopranos" and in the movies "Snakes on a Plane," "Evelyn" and "Ghost Ship."
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