Subaru 2003 Legacy - Manual (Page 110)

2-20
Child safety locks
WARNING
Always use the child safety lock whenever a child rides in the
rear seat. Serious injury could result if a child accidentally
opened the door and fell out.
HB2002BB
Each rear door has a child safety lock that prevents the doors from being
opened even if the inside door handle is pulled.
When the child safety lock lever is in the lock position, the door cannot
be opened from inside regardless of the position of the inner door handle
lock lever. The door can only be opened from the outside.