"The high risk of bias in the trials, variation in outcome measurement, and relatively low adherence with the interventions during the studies hampers drawing firm conclusions."

There have been other studies that have found effectiveness, and basically all agree on no downside.

https://www.mayoclinic.org/diseases-conditions/coronavirus/i...

As far as children, there are a lot more negative effects that can happen that aren't fatal. There is a lot we don't know still