Above I've presented some of my thoughts on points regarding the family's conduct raised here. In this post I'll present what I see as the possible circumstances leading to Joshua's disappearance, in order of the likelihood I tend to assign them.
1. In my opinion, the most likely first step at this time is that Joshua made his way out of the house through a door which wasn't fully closed, possibly as a result of people going outside to smoke.
1a. Once out of the house, perhaps he stumbled into an unknown cave/hole/septic tank or other small, hidden place which is either outside the current search range, or has been overlooked. In this weather, the dogs' accuracy is reduced, and any spot small enough for a toddler to curl up in could easily be small enough for searchers to miss.
1b. Or perhaps, having made his way out, he was taken in a crime of opportunity. I find the predator scenario possible, but less likely than point 1a above, made only slightly more likely (in context) by the proximity of a known SO. If the guy across the street had company at the time, I'm sure LE is all over that and any POI could be located without much trouble -- he would have been seen traveling there, or parked there, or cell phone pings would show another person, etc. As for himself, others have made the point that most criminals who victimize teenage girls are just not interested in baby boys, but of course it can't be ruled out. A complete stranger just happening to be passing by or lurking around the house is even less likely, but also can't be ruled out.
2. Another possible first step is that he was in some way physically harmed by someone present, accidentally or intentionally, and everyone is covering up for that person. I believe this is so unlikely as to be almost impossible.
To suggest that every single adult present -- including grandparents -- would feel more compelled to protect the killer of this child than to tell the truth, even to the point of participating in hiding his body, contradicts so much of what we know about human behavior and group psychology that it would require the revelation of some very solid evidence to seem at all likely to me.
It is extremely difficult to get nine people to agree on where to go to dinner, let alone how to dispose of the body of a cherished, innocent loved one, or keep a secret despite incredibly intense emotional pressure.
2a. However, with the noisy game on television and lots of social chaos, it is possible that the child was attacked or suffered an accident while only one or two adults were present. In this case, rather than being less likely, I believe the chance of a smaller coverup is actually even higher than normal due to the presence of so many other family members -- a person or two people might panic terribly at the thought of immediately revealing to close family members that a moment of weakness led to such a tragic consequence.
2b. It has been suggested here that the entire family somehow conspired in advance to make the child vanish. I include the possibility for completeness, but only because "maybe he was abducted by aliens who wiped everyone's memory" seems slightly less likely and I have to end the list somewhere.
