As long as it's not another Megan is Missing horror flick, I'll give it a shot.
What do you think about The Lovely Bones scenario, with or without the bunker? Could that have happened? The girls were taken from the area, possibly by someone they knew casually and who is familiar with the area ... where did they go? If it was a spontaneous event, why wouldn't they have been found in Maiden Lane? Police would have DNA evidence on the bodies, but still it seems like the obvious first choice for someone acting spontaneously. Where would someone take two children on a Friday afternoon if it was planned, not spontaneous? Are there any old farms in the area?
Did they have a two or three hour head start?
Any old farms, old garages or buildings that could have a hidden room in the floor? When the girls disappeared that day I thought of a movie I saw on tv several years ago. I can't remember the name or the actors in it.
The plot is a young husband and wife are driving across country, and stop for gas at a lonely gas station place. The man is gassing up their suv, the wife tells him she is going in to use the washroom.
She never comes out. He goes in looking for her, and nobody admits she ever came in the door. At the end some guy had her stashed in a room under his big shop. Movies usually don't bother me much, but that one sure did. We and I do not gas up at lonely gas stations any more.