Youngsters in a Huddersfield village were so disgusted by the amount of dog dirt they put up posters urging people to make sure they clean up after their pets.
But their dozens of laminated coloured posters have been torn from fencing and left scattered in the mud.
And volunteers who co-ordinated the display are outraged.
The display was organised by volunteers with Meltham Library who help to take children from Meltham CE School on weekly visits to the library to choose books.
To speed up their trip they use a short cut at the top of Green Lane and Clarke Lane which needs to be checked for animal faeces as it is used as a dog toilet.
Meltham Town Council has been campaigning to stop the problem by supplying bins and bags.
Before Christmas - following a particularly bad experience - volunteer and local town councillor Pam Murgatroyd explained the danger of dog dirt to the children and asked them to design posters that could be put up along the fence of the shortcut to encourage people to “pick up, bag it and bin it.”
She said: “The children did 47 amazing coloured posters which I laminated. My husband and I spent an hour stapling them to the fence along the route for the children to see on our visit. Several people passing commented on what a great idea it was.”
But less than four hours later the display had been ruined.
“They had all been removed and left lying on the wet ground in puddles, said Clr Murgatroyd. “We have retrieved some of them, mostly ripped and sodden.
“The children were so looking forward to seeing their work displayed and hopefully doing some good. They are going to be heartbroken when they see what someone thought of their efforts.
“How can someone do this? Can they not take notice of what the children were trying to say? Are they not aware of the harm our children can come to if exposed to animal excrement? Maybe we should have displayed them low enough for the dogs to read.
“The person who did this should be ashamed and hopefully exposed if someone saw them doing it.”
The school took to Twitter to condemn the vandals, calling the damage “shameful”.