"To give any credence whatsoever to the idea that Madeleine could have walked out on her own you would have to accept that she had gone out the back way, pulling aside the sitting-room curtains and drawing them again, then opening the patio door, the child-safety gate at the top of the stairs on the veranda and the little gate to the road – and carefully closing all three behind her. What three-year-old do you know who would do that? And we knew our Madeleine. She simply would not wander off like this." Kate McCann.
http://www.mccannfiles.com/id31.html