There is this movie or tv series from the 80s about a group of children near a lake that find an ancient device that was put there by the ancients. This device protects the earth from alien intruding the earth. But now these group of kids must make the device stop work or it will attack the desecendendts of theseancients.

Does it sound familiar? Any one knows the nane of this tv series/movie?

It is a sci-fi genre from the 80s or 70s