Very
https://dontforgetthebubbles.com/evidence-summary-paediatric-covid-19-literature/
" Notably, the China/WHO joint commission
 could not recall episodes during contact tracing where transmission occurred from a child to an adult. Studies of multiple family clusters have revealed 
children were unlikely to be the index case, in Guangzhou, China, Israel, the USA, Switzerland and internationally. Limited data on positive cases 
in schools have not demonstrated significant transmission, except within adolescent populations. Studies of younger children in schools have found 
low rates of transmission, but with very low case numbers."