According to wiki, the kids were instructed to do more than take care of the door and lights - they had to tend to the livestock, too. So at some point, some of them may have been outside.
Bizarre.
No one tends the stock that late at night so not buying that from mama. That had me thinking maybe the parents killed the kids and started the fire to cover it but dismissed that theory since none of the other kids let the cat out of the bag.
Why did they open presents before Santa arrived?