Gillian Kearney, the actress playing Emma Barton, seems far too young to be playing mother to the 3 Barton lads who must surely be in their 20's or maybe 30 for the eldest. She is only 42 so unlikely to have such grown-up lads!
It's not unusual for actors to play parts with a big age difference. (e.g. Clive Dunn was only 48 when he took on the role of Corporal Jones in Dad's Army). The casting director must have assumed that a bit of make-up would be sufficient to make Gillian Kearney look the age she's playing.
You could be right, Chris, though I think she needs a few more lines adding to make her look more convincing. Good link about the actress who was going to play Bethany Platt. She has a very young looking face, though the rest of her body might have given her real age away!
Tina O'Brien was 17 in real life when her character gave birth to Bethany, four years older than her Sarah Platt. She didn't lie about her age to get the part unlike the sacked Bethany character who is 25 in real life.
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