I'm trying to find a TV-series I watched when I was a kid - between 1996 and 2000, in Belgium. Unfortunately, I only remember a single episode, and haven't been able to find it online.
The story went like this: two school kids, a boy and a girl, figured out there were aliens disguised as children at their school, and that those aliens would try to abduct children for some nefarious purpose. Since abducting kids would of course result in heightened security and paranoid parents, they would attempt to abduct as many kids as they could in one time, then get out of there.
The protagonists did some further research, and it turned out the aliens had to meet some very specific and peculiar requirements for their abduction apparatus to work (and this is the part I remember best, because it was so weird): the kids needed to be moving rhytmically under a slowly rotating object.
Next scene, at a party, the protagonists confronted the girl that made a disco ball (because it would fit the criteria perfectly). The girl started crying, stating she spent hours glueing mirrors to a basketball. I don't remember if she turned out to be the alien or not.