The E12 had child safety locks long before they were fashionable. Flip the lever down and the door cannot be opened from the inside. Flip the lever up and the door operates normally.
The center of the 5 buttons on the drivers side power window control panel disables the rear power windows, another child safety feature.

Dale Beuning
dale_at_unofficialbmw.com, Bainbridge Island, WA
http://www.unofficialbmw.com/dale.html
1995 M3 / 1990 K75 RT / 1981 528i