3D from a child's mind..

Ok so after my parents took me to a 3d movie as a child I asked them why we don't have it at home. They replied that it was impossible but did give a small explanation as to how the current picture appeared on the screen.  I couldn't wrap my mind around the idea that it wasn't possible. To me, there was something done to the movie lighting ON film and then we needed the glasses to see the effect. I wondered why we couldn't simply pull down something (sheet of some sort)  in front of the tv to simulate the glasses for everyone. THEN I suggested if we can pull a sheet in front then why not inside of the screen, just behind the glass?