I can't remember where it happened, but a while back two little boys were playing hide and seek and decided to get in the trunk of a car. The other little kids didn't tell the grown ups that they couldn't find them. A few hours later they had the cops and people looking all over town for them. The next day somebody thought to check the trunk of the car, and they were dead. Stuff like that probably happens more than we know.
There's also this story about two boys in Greece who were playing in an elevator at a construction site when they got stuck between floors and couldn't escape. They starved to death and were found three weeks later.