That's because long COVID is a poorly understood and some of the symptoms (e.g. memory issues) are still not clinically associated with COVID itself (yet).

Basically, long COVID is just the persistence of symptoms beyond being contagious or even infected, but it's come to mean (via the media and elsewhere) other exceedingly rare and unusual symptoms that last longer -- some of which are not well understood.

Basically, if sever long-term effects do linger, they are very rare and almost entirely mitigated by vaccines. Moreover, long COVID isn't a big issue in kids because they are typically asymptomatic.

Give this a read!