The children from St Matthews Sunday School in Chelston raised the money doing the Torbay fun run in June.
The money was donated to the Post Pals Charity, which encourages people to write to youngsters with serious illnesses.
The children from the Sunday School raised a total of £160 in the run and sent half to Post Pals and half to St Peters Centre in Chelston where they have been holding their holiday clubs.
Judith Skinner, one of the teachers at St Matthews Sunday School, found out about Post Pals in a magazine and encouraged children at the Sunday school to write to the children, she said: "I thought it would be great to get the children to write to the children on the list.
"I explained to them that the children they were writing to were very ill and they may not get a reply, but they wanted to do it anyway.
"It has been going really well and we have even had some replies from some of the children.
"When we were deciding who to give the money we raised doing the fun run to they all wanted it to go to Post Pals."
"At this moment I have six or seven cards to go off on the post and all the children really enjoy writing the letters."
Judith looks on the Post Pals website and matches the children on there to children of a similar age at the Sunday school.
She added: "We make sure we send every child on the website a birthday card."
All the letters are written to care-of addresses to protect the children.
Post Palls can be found at www.postpals.co.uk