The former Ugly Betty star and husband Jerry O'Connell welcomed the two girls Charlie and Dolly in January.
The 36-year-old was cast as Roxie Torcoletti on the new ABC series two months after delivering her children. She said that she brought the babies with her when filming for the pilot started.
She told People: "They were with me every second of the day. I was still nursing and I was on a real strict schedule with them."
Romijn recently admitted that breastfeeding helped her drop 60 pounds of pregnancy weight.
Eastwick, which is based on a John Updike novel and a 1987 film starring Cher and Jack Nicholson, will premiere on Wednesday, September 23 on ABC.