You cannot 100% protect anything. I have a relative working in hospital, they are gowned in protective clothing at all times. We can not be so timid as to expect more than just normal sensible precautions. Do we anticipate a similar shut down if something similar happens in future years? What will you sacrifice, will you lose a house for the risk? Will you give up a normal education? Would, if you lived alone, never go out and mix and meet a partner, have some sort of normal existence? This is what we are imposing on people, and you've isolated 1 scenario ( that Sweden and other nations show evidence they have under control ) that you want us to focus on that destroys everything else.
Old people are vulnerable, but I really think the expectation that the rest of the world stops (and to be honest, it seems indefinitely) to cater for this one scenario is absurd. An indefinite period of a lockdown for children at this age is an unbelievable burden for their progress in life.
Are we ready for the social consequences? The suicides, the isolation, these will be happening.