Partners Andrews Aldridge has created its first Christmas campaign for the charity, which has in the past used EHS Brann for the project.
The mailing highlights those children who care for sick or disabled relatives.
It aims to create high levels of donation with what is usually Barnardo's most successful campaign because of the upsurge in public sentiment during the festive period.
Recipients of the mailing, some of whom haven't previously donated to the charity, see a picture of a young boy along with the line "Robert will be up at 5am on Christmas morning" on a reversible flap. Turning this over reveals the line: "Helping his mother to the toilet again."
The work plays on the emotions of recipients, associating a child's Christmas Day experience with their own memories, before revealing that this child will spend the festive period as a carer.
The mailing points out that there are thousands of children like Robert and asks recipients to donate gifts to let these children take a break or receive assistance with family finances. The mailing is in two stages and is supported by an e-mail broadcast that will go out later this month.
Steve Aldridge, the creative partner at Andrews Aldridge, said: "It would have been easy to position these children as victims; instead, we came up with the idea of positioning them as 'young heroes' - a worthy title, which pulls on the heart strings and praises them for the astonishing work they do."
Andrew Nebel, Barnardo's UK director of marketing and communications, said: "We are absolutely thrilled with this campaign. The standard of creativity we have come to expect from Partners Andrews Aldridge has again shone through."
The campaign was art directed by Paul Arrowsuch and written by Roger Morris.