(CNN) — An Illinois couple says thieves broke into their house and stole what they thought was a jewelry box.

But there was no jewelry inside. Instead, they stole the ashes of the couple’s deceased infant son. Now the couple are pleading with the thieves to return them.

Two casts of little billy’s hands and feet– along with his ashes– are all his parents have to remember their son, who died five years ago when he was just ten days old.

“Matt and billy were twins and billy was very sick from the beginning,” said mother Sue LaDeur. “They knew he was sick. So they were both born nine weeks early. And matt was was healthy, even though he was early. And billy had a lot of problems. So he passed away at ten days old.”

His parents built a small memorial to him on their dresser. But yesterday afternoon, someone smashed a window and broke into their Elmhurst home, ransacked it and stole a few things, including Billy’s ashes.

“That’s all we have,” said Sue LaDeur

“It’s all we have of him,” Jim LaDeur.

The family believes the thieves thought the box had jewelry in it. By now, they should know that it doesn’t and LaDeurs are hoping the burglars will have a heart and returned the ashes.

The LaDeurs are Catholic and point out that ashes must be consecrated and buried. The couple says they were planning to bury their son’s ashes with them when they died.

The parents say whoever has the ashes can return them to the crematorium or even put them in the mail.