Children's TV Programme

[MelvynP]

Does anyone recognise this show from the late 80's?

The setting is rural, some village or a small town, lots of outdoor/landscape shots. The story revolves around some alien slime/slug creatures that came from space and are eating the inside of the earth. They mask themselves as humans but they apparently could be sensed by children or something like that. I remember scenes where the main character/s entered one of the tunnels beneath the earth and lots of slime was dripping around.

Thanks!