In reply to yesbutnobutyesbut:
Thanks for your concern, but I think you're reading too much into the photo.
These are judgement calls we all make, so unless you know the precise bit of chain we're talking about then you might just have to take my word for it. In this particular location a bit of static sling - even dyneema - is fine as a backup to the adult physically spotting/guiding the child.
But it's a very particular bit of one pretty unusual route, so for the avoidance of doubt: don't use static slings on via ferrata kids. Perhaps it's actually a bit of an unhelpful photo