He said that, but never doesn’t mean ever. However, the dog/s did not track past the top of the drive-way, where the kids would have got on the bus in the morning. Assuming they walked. I’m beginning to think like you. Either they are secreted in a confined space on the property (my aunt orders water in for the well in the height of summer, gruesome thought). Or, they were carried out, (unconscious?) why no boot prints per se and why no backpack - maybe their boots were packed into Lilly’s backpack. If Lilly and Jack were not conscious, there would be no need to put their boots on, so packing them out with them means a concocted planned. JMO/MOO