That is not what you’re suggesting though. What you are claiming is that nothing precludes Madeleine having a fatal accident after falling off the balcony, lying at the bottom of the steps for long enough to leave cadaver odour, being discovered by her father, being hidden by her father, then again half-an-hour later when he carried her uncoverered body to the other side of town because he remembered seeing a convenient bin there, chucking thr body in then coming back and getting his wife to raise the alarm. I think there are plenty of non-independent witness statements which make that scenario highly, highly unilkely.
I think, to answer the initial question, it would appear that, due to the apartment apparently being left unlocked, the McCann's children were 'more vulnerable'. I understand that by creating the thread and posing the question you are demonstrating to us heathens that a window of opportunity did indeed exist, and that 'window' came to fruition for our abductor. Thus, by us admitting that their children were 'more vulnerable' we are, by default, admitting that the abduction is actually now more plausible to a degree.
Conversely, one could argue that, if one wanted it to appear that an abductor had been at work, then this 'window of opportunity' was required. It's at odds with the whole 'timeline' submission, but then that's explained by their reluctance to be cast in an unfavourable light by demonstrating wilful neglect.
I like typing these things out to straighten stuff out in my head, as I am convinced I am currently losing my memory - seriously.