Kate did state that when she went to check the children, the door was suddenly slammed shut by the wind and when she opened it, she discovered that Maddie was gone. If this is the case (and I'm assuming there was an abductor and let's say they came after Matthew Oldfield's visit), then the door would not be more open as it was apparently discovered by Kate, but more closed as the wind was blowing on the door from that direction. If the wind was strong enough to slam a door shut quickly after Kate opened it, the door would have been closed when she arrived. The only way I can see it being as Kate said, opened when she arrived and closing suddenly (and again, I'm going with the intruder theory for arguments sake) is if she missed the intruder by a matter of seconds, which I find very unlikely. Of course it could be argued that the strong wind could have come in "bursts" or "pockets" every so often, but I still think she would have discovered it closed otherwise as if was at least 30 minutes between the checks. I don't believe the sudden strong gust of wind that closed the door when she was there was the only one that night. I would also assume the door slamming would wake up the twins, but this is just my assumption.
I also think they would have found evidence of a third party on the window.
Basically, I think given the wind on that night, the doors would be more on the closed side than open side as was discovered (not including prior to the window being open) and again, assuming there was an abductor, I would think he would try to keep the room secluded and not have the doors more open if he were trying to do something illegal like that. Of course I could be wrong, and I'd love to hear what everyone thinks about the wind in relation to the window and what it could mean.
Given the wind as well, wouldn't it be more likely that the abductor would leave evidence such as hair and clothing fibres behind? I'm not an expert and I don't know for sure, but I would think there would be more chance of evidence blowing off than there would be in an environment that's not so windy?