This study was released a couple days ago:
" The estimated Rt was 1·28 (95% CI 1·26–1·30) during the 2-week period before the start of the school closures and 0·72 (0·70–0·74) during the first 2 weeks of school closures, corresponding to a 44% (34–53%) reduction in transmissibility (figure 3C). Similarly, the Rt calculated from hospitalisation data was 1·10 (1·06–1·12) before the start of the school closures and reduced to 0·73 (0·68–0·77) after school closures, corresponding to a 33% (24–43%) reduction in transmissibility (figure 3D)."
https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(20)30090-6/fulltext
There's not a lot of peer review out there right now, on any of the articles. But there are tons of cases, both locally and in many other states, of kids getting the virus and transmitting it among friend groups and to relatives.