In Hingham, Massachusetts, residents know of an abandoned tennis court which is covered with children's toys. Locals only go there when they have to. Its history baffles most of them. It is known as The Playground of Misfit Toys.
Unbeknownst to them, this area is likely a trophy yard.
Often serial killers who hunt children will specialize in children who are poor. Those are less likely to be noticed missing and their cold case files are frequently overlooked. If the serial killer has a dumping ground where the bodies are never found, the cases may vanish into the vast cloud of missing persons cases filed every year.
The toys are trophies of the serial killer's victims. Each of these children probably had one toy that was sacred to him or her. The killer can watch the child from a hiding place to find out what toy the child values the most. Then they approach the child and hold the toy hostage.
"You can have your Big Wheels back... but only if you come with me."
So they come to him, pairs of children and toys. When the child is killed, the serial killer relishes his trophy. And yet there is no tension in that, no fear of getting caught and none of the thrill of the game. He displays them in public to bring back that thrill. The risk and forbidden nature of the crime thrills him as he re-lives the delicious moments of the kill in his mind.
He puts the toys there to see if anyone will notice, care, and connect the dots. To see if it will bring them back to him.
Because soon... he must kill again.