Saying Goodbye features the stories of a group of children and young people in the UK dealing with the terminal illness or death of a parent.
The King’s Speech actress said: “It’s a privilege to be able to be involved with such a heart-rending film which shares such honest and important stories from children and young people as they cope with death of a parent or are facing this possibility.
“I hope this film strikes a chord with people across the UK and encourages them to donate to BBC Children In Need to enable the charity to continue to support children and young people who need it most.”
More than 100 children experience the death of their mother or father every day in the UK, according to the BBC1 programme.
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Many of the children in the film have been supported by projects funded by BBC Children In Need.
Two of those featured in the film include sisters Imogen, 12, and Madeleine, nine, from Hengoed, South Wales.
They share their experiences preparing for the loss of their mother, who has an incurable form of breast cancer, which can be inherited.
Their father also has a life-limiting illness, Huntington’s disease, a genetic condition that damages nerve cells in the brain.
Discussing her mother’s attempts to prepare her for life without her, Imogen says in the film: “If she’s not there I call her every night. And she says, ‘You need to stop doing that so that you’re ready for the future - because you can’t just call me up once I’ve passed’.”
It is hoped the film will help children and young people in similar circumstances.
:: The film will air at 10.45pm on Tuesday November 14 on BBC1.