The actress, 34, posted a photograph of Tennant, 48, holding the new born in a car seat while leaving the hospital.
In a nod an event that takes place at the start of the show, which sees Sheen plays an angel while Tennant plays a demon, Moffett joked: “An angel, a demon and a couple of babies. What could possibly go wrong?”
Many people shared their congratulations on the post, including actress Tracy Ann Oberman.
She commented: “Aw congrats”, while another Instagram user added: “CONGRATS! To the new mothers and fathers!”
The couple, who have been married since December 2011, welcomed their first child together in March 2011.
Happy to say that at 8:41 am on Monday September 23rd our beautiful daughter Lyra was born. Thank you so much to Louise & all the brilliant midwives at both the Singleton and NeathPortTalbot hospitals. ❤️👶🏴🇸🇪😍 pic.twitter.com/Y4Xdt7GkMz— michael sheen (@michaelsheen)September 30, 2019
Moffett has another son, 17-year-old Ty, from a previous relationship, who Tennant adopted prior to the couple's marriage.
Ty has followed in his parents’ footsteps and is also an actor, who will feature in the latest TV adaptation of The War of the Worlds.
He previously starred in the J.R.R. Tolkien biopic, Tolkien, starring Nicholas Hoult and Lily Collins.