Second - while I agree with your assessment of what might happen when you are in a panic, generally speaking, when a person finds themselves in such a position, it is not uncommon to: 1) check self for injury, potential harm and react accordingly; 2) once self is covered, do a mental check of where those of importance might be - run through your mind wife/husband/children/parents; 3) at this point - if you are safe, almost always you will check to be sure your "immediate" others are safe. As a parent, this is your first priority, it is second nature; 4) you do what is necessary to protect your "immediate" others.
I do not believe a parent, who just discovered her child missing, would abandon her 2 other children, even for a moment. There were so many options here.... picking up the phone, standing outside the door and screaming, taking the children with her. Having given this quite a bit of thought - picking up the phone might have seemed like a "nonoption" knowing the person on the other end would speak Portugese, not English - discard this immediately because you have no time not to be understood. Standing outside the door and screaming - definite option, after all the Tapas Bar was within sight of the apartment, but maybe being of a more reserved culture, this type of behavior would be unacceptable to a panic'ed mind. Picking up the remaining 2 children and running for cover - totally acceptable on all accounts, except one... leaving the apartment without knowing where the 3rd child was. To my mind - it would be extremely difficult to walk/run out of that apartment not knowing where the 3rd child was.... Having gone through the safety issues related to my "immediate" others - GM waiting for me, twin 1 in bed, twin 2 in bed, Madeleine missing....., double check, still missing, twins still there, okay... I need help.... she's not in the bathroom, she's not under the bed, I need help.... where is she, need GM, what do I do? what do I do? phone - they won't understand, call GM - he doesn't have his cell phone (I don't have my cell phone), call him from the door (then I'll make quite the scene), go get him.... go get him.... the twins, what about the twins????? what do I do??? I need GM, Madeleine is missing, I need help.... go get him.