I listed sources in my original comment. From the first link, they observed 4.8% of lab-confirmed cases exhibited continuing symptoms, and the average effect on cognitive performance was 0.47 standard deviations (equivalent to about 8 IQ points, or roughly the effect of a stroke). The CDC study has some methodological problems (detailed in nradov & DannyCasolaro's sibling posts), but previous meta-analyses have documented similar effects; they covered only severely-ill patients, but came up with a pooled proportion of 14%. Chronic fatigue is reported as a symptom 6 months following in 46% of cases [2], but again, that study is for adults.
[1] https://www.npr.org/sections/goatsandsoda/2021/11/18/1055071...