Max and Harvey Mills play Thomas
Identical twins Max and Harvey Mills became instant stars when they arrived on set to play William and Mary's 18 month old son Thomas.
Their sunny, happy go lucky natures, made them a big hit with all the cast and crew, and won them a big round of applause when they completed their final scene.
"Harvey used to bound onto the set shouting 'hello' to every one, and Max would saunter in behind being cool. It was like being in a big family environment, and they were very happy go lucky. They treated the house where they were filming just like their own home," says their proud mum Sara Devey.
"Before we started filming I had shown them pictures of all the actors, and taught them their character names, so they would know who everybody was. They quite happily called Julie 'mummy', and Martin 'daddy'.
"On the last day of filming the boys were given a big round of applause as they finished their last scene. It was quite an emotional moment. The cast and crew had been like an extended family for the boys. During filming they saw more of the cast and crew than they did of their own grandparents. It was a bit strange for them getting up every day after filming, and not seeing all their new friends."
Max and Harvey, who celebrated their second birthday in the middle of filming, were among 12 sets of twins who were auditioned for the role of Thomas. The twins were required to take it in turns to play the part to ensure the rules of filming with children were adhered to.
"The producers told me they were looking for little boys who looked like Martin Clunes. When Martin saw them he joked 'I hope their mum doesn't come after me for paternity!'," says Sara.
The boys didn't always do exactly what the director wanted. For one scene Max had to play peek-a-boo in bed with Martin and Julie, and he clearly wasn't keen on the idea.
"To make Max play I crawled under the duvet with him, and Martin and Julie. It was hilarious to see all four of us in bed!" says Sara.
She had another secret ploy to make her boys perform perfectly for the cameras - boxes of raisins hidden around the film set.
"The boys love the raisins, and I knew it would be a good way of encouraging them to do things. The director said it was the first time he'd had to say 'cut, more raisins please!'"
Although the boys are identical, Sara can obviously tell them apart, and she dresses them differently. Harvey usually wears reds, oranges and purples, while Max wears yellows, greens and blues.
But Sara confesses: "When Max and Harvey were on set they had to wear the same clothes, and even I had to stop and look twice to work out who was who."
Sara and her partner, Paul Mills, met when they were working on a cruise ship together. They worked as film extras when they returned to England. Then Sara discovered she was pregnant with the twins. The boys were born on New Year's Eve, four weeks early.
They had their first taste of the limelight when they were just a few months old, in a photo shoot for Hello magazine with television presenter Alice Beer, to promote the Twins and Multiple Births Association.
Max and Harvey went on to make their television debut in a BBC drama with Sheila Hancock. The family lives in Berkshire.