What is the best exercise for teens to do their immune system better?

This lockdown is a very crucial time to fight the coronavirus. So it is important for us to stay at home and prevent the spread of coronavirus.
So we have to keep in mind the environment to keep our teens healthy amdist this lockdown.
They should be made to exercise rdd regularly. Exercises like skipping , stretching, situps etc. Should be done by the teens. Even we ,parents, should accompany them in the exercises firstly to keep ourselves fit too and secondly setting them a personal example and as a source of motivation for them to carry on with the daily exercises.
They should be fed a balanced diet. Proper food , even during these lockdown, should be provided to the children so that they remain healthy. If possible juice, curd, all sources of protein and especially green vegetables should be provided to the children through appealing yet healthy foods.
Sleeping patterns should not be changed.
Proper sleep even during this lockdown should be maintained. Timely going to bed and waking up should be maintained to ensure a good quality of rest to the kids body.
Other than just food and physical exercises, mental exercises should be done. They should be made to play indoor games to keep them rejuvenated even when they are restricted at home.