This isn’t a paper, it’s an editorial, and it’s utter trash, printed in a bad “journal” (New Scientist is essentially a mass-market magazine, on par with Discover). The only evidence advanced for the claim is this:
https://www.medrxiv.org/content/10.1101/2021.01.23.21250375v...
This is a survey of parent-reported symptoms in 129 children, and of the “long-term” symptoms, all are vague, (e.g. headache, fatigue, muscle pain) overlapping substantially with the aches and pains of daily life.
They don’t even bother to link to it directly in the editorial; they simply mention the doi in the text. This wasn’t even proofread by an editor.
"Evidence from the first study of long covid in children suggests that more than half of children aged between 6 and 16 years old who contract the virus have at least one symptom lasting more than 120 days, with 42.6 per cent impaired by these symptoms during daily activities. "
There are folks that are still debilitated, almost a year after their "recovery". We don't know if/when their sequelae will disappear. Time will tell.
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7927578/