The boxes for beach toys were made by Orange Box Alnwick and placed at Boulmer and Howdiemontsands.
However, visitors have been using them to dispose of unwanted goods – and even dog dirt.
Regular beachgoer Jane Hardy said: “The idea is people use and return the toys for other children to share.
"It keeps plastic off the beach, reduces the need for families to buy plastic toys and means parents have less to carry when taking young families to the beach.
“(Recently), a swimmer removed a whole Ikea bag full of rubbish from the toy box at Howdiemontsands and dog walkers cleared the box at Boulmer of rubbish – it’s got a bin right by it.
"Occasionally I’ve even removed bags of dog excrement which someone has put in with the toys.
"What is the mentality behind deliberately contaminating something meant for young children? Please take your rubbish and dog poo home or use the bin at Boulmer.”
Jane, who volunteers with wildlife charities British Divers Marine Life Rescue (BDLMR) and Pawz4Thought, added: “We are fortunate enough to live in an Area of Outstanding Natural Beauty and we need to look after it.
“I’m forever rescuing wildlife caught up in our litter and lost fishing gear.
“It’s just common sense really to not leave your rubbish to spoil it for others. To put bagged dog dirt in a child’s toy box is an exceptionally unpleasant thing to do.”