1) There were net curtains & closed fabric curtains blocking the light from entering the room from outside so the petty thief would not have been able to see the children.
IMO having opened s+w the petty thief would pull curtains aside to have a look at the room he is planning to climb into.
2) That leaves another option - Madeleine awoke, started crying & that disturbed him.
Agreed on disturbed. But I think maybe by movement. IMO the natural reaction in those circumstances would be to
not make noise, but to go into another room, there was a USA "kid home alone in same room as attempted entry" case where the the response was: no cry/scream, go to another room and hide.
Madeleine would not have seen someone opening the window & shutter due to the curtains- she would only have heard it.
Good point, I am not sure about the visual, but the point is if you wake up to someone opening a noisy shutter you are definitely going to hear it, whether you see it or not too is debatable (I think you would), but no matter, the obvious response is the same in either case.
So, did she flee into her parents' bedroom,
I don't know but that's not inconsistent with the instinctive room in other khaisraae cases like the one I referred to.
screaming for mum or dad like most children would? On finding her mum & dad missing, would she not have screamed even louder? Yet nobody heard anything - not Mrs Fenn, not the Moyse couple, not Jez, not the Tapas checkers.......
Again a good point, but IMO if I wanted to not attract attention I would make as little noise as possible.