The only person to blame for her disappearance is the person or persons who abducted her. Whether you're happy to leave your kids alone in a room and how far away you're happy to be is entirely your choice. Should you be the highly statistically unlikely parent who has a child abducted by a stranger, the fact that you weren't in the room when it happened will be punishment enough for you for the rest of your life.
Kate McCann often came across as cold and emotionless in the months subsequent to Madeleine being abducted during media interviews and this has coloured many people's views of them as a couple.
A huge amount of money has been invested in private investigations by the family and this has been raised by them in whatever way they've managed. I assume that with their level of education and background, they've possibly had more resources to call on to enable them to raise this money. I assume polis are obliged to look into the no doubt tomes of information that has been passed to them from investigators.
Saying they are "firmly to blame" is plain and simply wrong. I notice druidh hasn't hung around to defend the statement so I can only assume he's trolling, and in pretty poor taste.