I can see the blanket being planted or being left by the kids, but most likely imo it is unrelated and just happened to be there for one reason or the other. Because if you would want to stage a kid getting lost in the woods would you place a strip of an old blanket you never even mentioned before in the trees near the road? Or would you put the backpack you said the kids had with them somewhere in the woods? One of the wellies you said they were wearing in a body of water? A hat, sunglasses, a glove thrown on the road to stage an abduction? Or place the bigger part of the blanket by the side of the road at least? IMO a piece of blanket you did not say the kids had hanging in a tree by the road makes no sense for trying to indicate that the kids were lost in the woods, drowned or were kidnapped. It indicates nothing. It is not even something the kids had in active use, as far as we were told.
I think it is quite likely that people in that hood were eermh not terribly careful with discarding their old items properly. (Additionally, what it first reminded me of, was how we mark "entry/exit points" in the woods - you tie something to the trees at around 1-1,5m high, to mark, that this is the turn, either something reflective for car drivers to see narrow service roads properly or some string or similar in the actual woods to mark your walking trail - but as no trail was mentioned and it was not tied, I don't think this was the case here.)
I am still most intrigued by the Lilly-sized boot print. That is IMO more likely to be either a sign of the kids or something planted. How many 5-7 year old kids could there be in such an isolated place that just so happened to be walking in the wilderness near the Sullivan home? If this was one of the searchers, they would know and have ruled it out in no time. While a piece of blanket can end up on a tree with the help of wind or a crow or a squirrel, a boot print indicates human presence at the very least. Now it is possible it is, say, made by Lilly but notably older than the day the disappeared. But even then it is interesting - had the kids been wandering that far away previously? It is also possible it was made earlier by someone else, but I have a feeling they would know that as well, as there are just so few people around. It is also possible it was a planted imprint - in this case, one can think when this could have happened, who could have been at the location alone and where would the boot have been hidden (maybe before and) after. It would still be way easier to just chuck the backpack in the woods, though. But then again, a backpack left behind would indicate the kids are not fine. A print is a happier sign - they are somewhere here, they were just walking here.
Dunno. All this essey to say, that IMO a childs bootprint in the woods is more interesting than trash in the trees.