this is untrue. Israel also opened their schools and saw a large jump in school and societal cases of COVID-19.
Correct, and schools in Europe didn't fully open months ago either. They gradually opened, shortly before summer holidays, so any outbreaks could be more easily managed. Now (last week) 1/3rd of the schools in my country have started opening up, with lots of (distancing and hygiene/masks) precautions and additional ventilation (not recirculation). Testing capacity should be able to quickly detect any outbreaks and contain them.
I also find it shortsighted by some to only focus on the lower casualty numbers with lower age, since children can be the ones that infect their surroundings (teachers, parents, grandparents, other family and neighbors). And also, some children do get very ill, and may (unlike most influenza cases) suffer the consequences for life.