It's Japanese taraditional exercise everyone knouws in Japan.
During summer vacatin of elementary schools, we woke up early and gathered in parks or open spaces. There, we did exercise listening to radio music and directions.(I forget accurate time, but I think it started from about 6:30.)
If we joined the exercise, we could get stamps and sometimes sweet treats.If we complete the stamps, we coule get some stationeries. I had tried complete them, but I never because getting up early was so difficult for me.
I think childern gatherin in early morning and doing same exercise look strage for foreigners, but it reminds me elementary school summer vacation.
If you have interest about this, refer to following link. This is a TV version.
After I found this link recently, I do this sometimes.