Country of origin: Probably the U.S., it was aired numerous times on HBO.
Date: From before 2000, probably 90s or 80s.
A family moves into an idyllic apartment complex where everybody is happy and upbeat. One of the kids (a girl?) finds out somehow that the population they've entered is secretly being sedated by a sect/cult/organization, in order to maintain the pleasant environment.
It's a "B" category movie, could be a made for TV pic.
The Colony (1995)
The Stepford Wives (2004)