The trouble with these kinds of articles is that they invariably start out by showing a family with some poor child who is severely ill and cannot do normal activities like walking unassisted, and then they follow up with ".. and XX% of children have this syndrome," skirting over the fact that the majority of kids being included in this group are still just suffering things like headache or fatigue a couple of months out, and very few (thankfully) are like the unfortunate child being portrayed.
Of course long covid is a concern, but can we be careful not to dissolve into a kind of moral panic here?
The BMJ has already pointed out the issues with the paper in question. The study does not even appear to have a control group---meaning it's not factoring in the fact that at any given moment in time, a certain percentage of any group of people (who have never been near this virus) will have issues with headache and fatigue and things like that. Unless you compare with control groups it's impossible even start working out how many of the headaches or whatever could be caused by other things.
www.bmj.com/content/372/bmj.n157/rr