Most mums with children under a year old would feel strange seeing another woman mimicking their role, especially if it involved lying in bed feeding those children and even rocking them to sleep.
But when that woman is actress Olivia Colman and the mimicking is done for a hit TV series, it's exciting too. So says Emma East, 24, from Hertfordshire, whose twin girls Isobel and Sophie play the part of Katie, the new baby born to Olivia Coleman and Tom Hollander in the third series of the BBC comedy series Rev, which started this week.
"There's no doubt it was bizarre seeing someone else, essentially a stranger, playing mum to my children. And it's been equally strange seeing Olivia on the front of magazines this week with my twins, posing as their mum. But of course, I was present the whole time and it has to be said that Olivia was a real natural, having had children of her own," says Emma.
The same cannot be said of Tom Hollander, laughs Emma. Indeed, when recently interviewed for What's on TV? about what it was like playing a father of a baby, the Oscar-winning actor said, "We used twins actually and they were a delight eventually. They were pretty frightened of me!
"I don't have children myself and I'm not very confident with them and it got to the point where they would see me and start screaming. But with the miracle of editing, she is very cute and makes a significant contribution to the scenes that she's in by looking very strangely wise in the way babies do."
It started off well, recalls Emma. "But I think Tom felt really pressurised to be good with the babies – something he wasn't used to – and the more he became nervous of them, the more the babies picked up on it and that would be enough to make them cry around him. I remember being quite stressed about it actually.
"I didn't want all the crew thinking Isobel and Sophie were really grumpy kids. Also, because Rev is Tom's baby – he co-created it as well as starred in it – I didn't want him to regret writing babies into the script or choosing my babies to play the part.
"But in the end, I thought, 'This isn't something I can control' and we all relaxed about it."
Emma says she was thrilled to bits when they picked Isobel and Sophie to star as baby Katie. "We'd signed our three-year-old daughter Olivia to a children's agency as a result of me appearing in a TV programme about breastfeeding when she was a baby. BBC3 decided they'd like me, my partner and Olivia to appear in an ad for the whole series and that meant we needed to belong to an agency."
Olivia was soon invited to a whole range of castings including for a Mothercare catalogue, Downton Abbey, a John Lewis ad and a British Airways campaign.
"She didn't get any of those, but she did get picked for a Sainsbury's ad and there was quite a lot of money involved, despite the fact that neither us nor Olivia had to do much. It just seemed a great way of getting some savings together for when she's older. With the twins, it made sense to do the same."
Emma and her partner Humphrey chose the agency carefully. "We'd seen a TV programme on things you have to watch out for with dodgy agencies, such as astronomical joining fees, and Bizzykids was the one name that kept coming up as responsible. The joining fee is £180 for 18 years and you have to take some pictures when they hit four, but that's it."
Emma insists that children are not picked purely on the basis of cuteness and attractiveness. "The casting directors usually have something quite specific in mind, but it's not usually stereotypical looks.
They go on their behaviour too – probably one of the reasons Olivia was turned down for a lot actually, because she can be quite shy and under confident around strangers."
Emma didn't get any work offered for the twins until one day she got the call about Rev. "The agency said they were looking for nine-month-old identical twins with dark hair and that's exactly what they were.
"We were just incredibly lucky and we pretty much knew they got the part as there were no other babies at the casting."
When the call came through, Emma was ecstatic. "We liked the actors and the programme and we knew it would be a lot of savings for them in the bank. I got paid a daily rate as their chaperone too and what's more, we were picked up every morning and driven home too."
There were 19 days of filming altogether over a 10 week period. "I was nervous on day one. I didn't quite know what to expect. But there was always a private room with toys that we could be in when the babies weren't in the scenes, regardless of whether we were filming in a pub or church or vicarage, and the crew were all really friendly.
"It was also fascinating because you don't often get to see behind the scenes of a show you really like. I looked forward to going to work and the babies, for the most part, loved the attention and stimulation."
One of the funniest moments for Emma happened when they filmed Tom holding Sophie up to the stained glass window in the church. "It was one of the first scenes and Isobel was still a bit nervous. So they had me hiding behind the alter, from where they wanted me to jump up quickly to make Isobel smile. I jumped up at completely the wrong moment and ruined the whole scene, but everyone laughed."
Rice cakes were a saviour throughout the filming, chuckles Emma. "It kept the babies happy, but there was one scene where Olivia was holding Sophie and she was trying to deliver a line, but Sophie keeps interrupting by shoving rice cakes in her mouth. Again, we did laugh about it."
Although Emma is not at liberty to disclose the plot, she does say there's one scene towards the end of the series which will be a particularly lasting and personal memory for the babies. "Tom did something really nice that he didn't have to and I found that very moving."
Emma was thrilled to be invited to the wrap party. "The filming took over our lives for 10 weeks, so it was a nice send off. And I felt honoured to be invited to the screening too, which aptly took place in a church. It was amazing to see how it had all come together because they hadn't filmed the scenes in chronological order. It's very funny and really good."
This week has been exciting too, what with the build up to the first episode airing. "The babies have been in the Radio Times and What's on TV, among other publications, and so I'm putting together a scrap book for them to keep.
"I think I'll actually feel quite sad when the series ends as it's wound up meaning quite a lot to me."