Babies delivered in the new PBS series “Call the Midwife” are largely fakes, the executive producer says. “We had a number of prosthetic babies made, which I have to say were incredibly convincing, and they are quite disturbing, actually,” Hugh Warren told reporters at press tour.

“They are really heavy,” says the series star Jessica Raine. “And we had one baby with a detachable willy, so it could be a boy or a girl baby.”

On screen, though, they are effective, she says.

“It’s all angles,” she says. “And you pretend to maneuver it out of the woman’s body. So it’s really clever. I can’t believe how good it looks, because you are doing it going, ‘This is crazy. Is this going to work?’ And, obviously, I’m not by the monitor. And everyone is, ‘Huh,’ like that at the monitor. So it is working.”

“It still amazes me that you see the sleight of hand going from the prosthetic to the real baby,” Warren says. “Because we used a lot of newborn babies, obviously. It’s so effective that you feel like you’ve really witnessed it.”

Set in the early 1950s in London, “Call the Midwife,” already a hit in the UK, runs Sundays at 8p.m. on PBS.