The stars were photographed to promote the charity's Christmas Jumper Day campaign, encouraging people to sport festive knitwear for a day and donate to support some of the world's most vulnerable children.
Copyright: Save the ChildrenChannel 4 News anchor Jon Snow and This is England actress Vicky McClure are also among the celebrities who are supporting the fundraiser, which will take place on Friday, December 14.
Klass said in a statement: "Save the Children's Christmas Jumper Day is the perfect excuse to wear your festive woolly with pride, whilst helping to save children's lives.
"I've visited Save the Children's work in Bangladesh, so know just how far your donated £1 can go. I'll be buying crazy knits for my friends and family to ensure
they are all taking part on December 14th."
Snow added: "It's not always easy to demonstrate commitment to the festive spirit, but who can argue with a reindeer sweater?
"The money from Christmas Jumper Day goes towards a great cause - saving children's lives - there's no excuse not to dig out your funniest winter knit and wear it with pride."
More information about Save the Children's Christmas Jumper Day can be found at www.savethechildren.org.uk/jumpers and www.facebook.com/xmasjumperday.