Let's look at the U.K. which has devoted significant resources to identifying and studying Long Covid cases.
"The latest ONS report, released earlier this month, showed over 117,000 children live with long Covid in the UK, 117,000 that could be living with symptoms of Covid for the rest of their life."
'Much worse than anything else': Expert on the hidden impact long Covid has on children
https://www.express.co.uk/life-style/health/1582833/covid-long-covid-symptoms-children-ons-report
But none of this should be news to you... this particular has been posted to this thread previously -- while studies have been provided to you pointing out the numbers and devastating impact of Long Covid.
That's the flaw with "how many children / adolescents" have Long Covid because the only measurement we have is by a small subset of the population that was part of a study
or research group.
Simply, most initial Pediatric Covid cases are
mild illnesses (e.g. cough, running nose, a little fatigue), especially with Omicron. Many of it goes unreported by the family except for cases that the Covid infection spreads to other family members like the adults or people went to emergency care due to the Covid illness became more serious.
With Omicron, many families in the United States and Canada were sent those
free home Covid tests and told to self-isolate / quarantine if positive. Thus, I doubt people called their Doctor or some number to report a positive test for a mild illness like a cough, running nose,
or a little fatigue until the Covid illness progressed into something more serious that required medical treatment.
Thus, a study / research group of lets say 200,000 children / adolescents with Long Covid
does not imply those are the only individuals with Long Covid. Instead, those are the ones that volunteered to be part of the study.
My neighbors entire family became infected with Omicron and all of them only had a mild illness. They only had one of those free Covid home test kits and they recovered quickly without needing any further medical care.
- I did ask them if they reported their test results to the local public health agency of Québec. They responded that it was not needed because it was very mild.

Now if one of them develops long-term symptoms like consistent breathing problems, consistent headaches that last several weeks
or months after they no longer have Covid. There's a good chance they will be treated for that illness and it will
not get diagnosed as Long Covid unless it developed from a Covid infection that required hospitalization or required medical treatment.
wrbtrader