The highest quality study on this to date [1] found no difference in the prevalence of long term symptoms between kids that had covid and kids that didn't.
He states that '4% seropositive having symptoms after 12 weeks', but omits to mention that 2% of seronegative have symptoms after 12 weeks too...
Also he doesn't mention the 9%/10% rate split at 4 weeks, or the symptoms:
Tiredness, Headache, Congested or runny nose, Stomachach, Sleep disturbances, Cough
So he's making the case for child vaccination on the basis of 2 extra seropositive children having one or more of the above symptoms.
And, BTW, the study authors themselves note the limitations as follows:
'Limitations include the relatively small number of seropositive children, possible misclassification of some false seropositive children, potential recall bias, parental report of child’s symptoms, and lack of information on symptom severity.'
The study authors concluded that:
'Seropositive children, all with a history of pauci-symptomatic SARS-CoV-2 infection, did not report long COVID more frequently than seronegative children. This study suggests a very low prevalence of long COVID in a randomly selected population-based cohort of children followed over 6 months after serological testing.'
[1] https://www.medrxiv.org/content/10.1101/2021.05.16.21257255v...