How to help (very) low-rated children "Get it" ?

Yeah there is some hyperbole here. I think even at 900 uscf you have quite a good grasp on not hanging pieces, but you need a few more hundred rating points to get that consistency down. A lot of chess is becoming so consistent that you don't make mistakes that "you know better about," to the point where that kind of mistake doesn't exist in your game anymore. Nevertheless, even Petrosian hung his queen once.

Good point.

I see this even in higher rated players, like 1600, where they maybe start feeling creative (or something) and it just completely backfires.

Maybe we all do it to some degree without realizing it.

Look at my last game. I resigned after my third hanging piece.

No hyperbole from me, if that's what you were talking about.

Absolutely not. If you look at the rating lists for children that are approximately 8 or 9, you will see some fantastic results, with the lowest rating being 1400. 

What rating lists are you talking about?  The vast majority of 8 to 9 year olds are rated well under 1000.

He's probably talking about the top 100 lists.  They list the 100 best 8 or 9 year olds in the country.  There have been 9 year old masters.  But they started playing when they were 4 or 5.  8 and 9 year old beginners are not going to be on these lists.

There are probably tens of thousands of 8-9 y.o. USCF registered players (several hundred just in my area) and I'd bet the average rating is 400-500. Top 100 lists aren't exemplary of the entire age group.

Bottom line is kids that age and with little tournament experience hang pieces. At least some of your kids are seeing the hanging pieces and take them! I'd just keep repeating over and over the importance of piece safety.

"dumb" the game down for them. Focus on building blocks.. and make connections with material to help make a grasp.. if you just create isolated examples like this is "fork" or "pin" etc. they not be able to connect it to a tangible situation or in different contexts, because they may not fully grasp it. If you get too caught up on those concepts.. well they can also be a bit too much of a segue to openings or simple postional/ constructive moves. I would focus with them on the opening and the purpose behind each move to understand why each move is important, but not disable them from trying out their own openings without discouraging them by exposing the weaknesses. 

Start with simple things such as a pawn race - whoever gets the pawn to the other end of the board first wins - then when they have got the basic grasp of that do the same with rooks on the board etc. But as has been pointed out before many off the kids may never 'get it' through simply lack of interest or lack of natural chess talent. Usually if a young child displays a degree of aptitude for the game then it is easy to spot early on.

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