Read Jeremiah 7:30-8:3
The shrines of Topheth, which means fireplace, were set up in the valley of the son of Hinnom, where debris and rubbish from the city were thrown away. This altar was used to worship Molech; a god who required child sacrifice (2 Kings 23). Their valley of sacrifice would become their valley of slaughter by the Babylonians. At the place where the people had killed their children in sinful idol worship, they themselves would be slaughtered.
The threat that the graves of Judah’s people would be opened was horrible to a people who highly honored the dead and believed that it was the highest desecration to open graves. This would be an ironic punishment for idol worshipers; their bones would be laid out before the sun, moon, and stars, the gods they thought could save them.