When I was in second grade, my mom dropped us off for summer camp at a ranch in South Texas. I remember crying and clinging onto her, trying to talk her out of it but she left us anyway and I'm glad she did. We spent the next two weeks riding horses and playing in a muddy swamp and doing leather crafts. When she came back to pick us up, we probably cried twice as hard because we didn't want to leave. The next summer, we stayed for three terms (six weeks).
I hope that this German idea takes root here and an anti-helicopter trend starts in the US. I do everything to raise my two young sons (2 and 5 years) in an environment where they're allowed to take risks but it's tough because this attitude is shared by so few of their friends' parents, even here in deeply red small-town Kansas.
EDIT: Just remembered about the sweet outdoor preschool on Vashon Island in Washington State. Check this out: https://www.seattletimes.com/seattle-news/outdoor-preschool-...