I remember watching a movie where, in the beginning, the government gave a seven kids or so to aliens in a UFO. In the midst of the abduction, one runs away and escapes abduction. I don't recall too much of the plot but at one point there is an scene where people have an alien behind a piece of glass, but they are unable to see it because of green smoke. The people try to talk to it and it is angered and bangs a crablike appendage against the glass. Eventually one of them goes into the room where the alien is and discovers that it is actually a previously abducted child (Lumier, I think) who is hooked up to a machine and fed drugs by the abductor aliens. This may be another movie but I think at one point kids start repeating numbers which signify how many children the aliens want to abduct.
Could this be Torchwood: Children of Earth?
The plot of Children of Earth deals with aliens demanding the Earth's children, and a related earlier conspiracy 40 years ago; as such, Torchwood is pitted against the British government when the government attempts to conceal its past actions and concede to the present-day aliens' demands.
You can see the scene you're referring to below.
All the details add up to this, except that the children are basically the source of the drugs that the aliens in the box are consuming. That's why they want them - so they can provide them to others of their kind. They're basically drug dealers trying to re-up their supply, and scaring the shit out of the people of Earth into doing it.– DerekJun 10, 2022 at 9:16