On June 26, 2020, the U.S. Department of Labor issued Field Assistance Bulletin No. 2020-3, clarifying that, for purposes of federal child labor laws (which dictate hours of work for minors), schools that are “closed” for COVID-19 are “in session” so long as the child is required to participate in virtual or distance learning. While summer school is considered “outside of school hours”, if a school district makes summer instruction mandatory to make up for lost instruction time due to COVID-19, then summer school is treated as an extension of the regular (mandatory) school schedule for purposes of hours of work for minors. I am currently unaware of any Minnesota district that is doing this, but for Minnesota employers doing business in other states, it is something you should certainly keep in mind.