Basically, from google searching the youtube link, I immediately found a facebook post. A woman called Miya Moro has posted about a conversation she had with somebody online, about an elementary school singing competition. The person says he/she were very moved by the kids. Apparently they sung nursery rhymes. The songs were very touching according to him/her. Miya says:
It turns out that the nursery rhymes in Japan are full of the most beautiful nature and childlikeness. She then starts thinking about memories of nursery rhymes while she was in elementary school. She has no memory of such songs, although she ought to have heard some. And since she doesn't remember them, Miya decides to look some up on youtube. Turns out they are Taiwanese nursery rhymes. And this one in particular is called "
泥娃娃", which (according to google translate) translates to "Mud Doll".
So, it's not an anime but nursery rhymes. Still, they sound very nice. Pity I can't understand what's being sung. But if you are interested in seeing what exactly Miya Moro said, here's the link to her facebook post:
You must be registered for see links
Screenshot_20200212_212454.jpg
Screenshot_20200301_023126.jpg
Screenshot_20200301_024310.jpg
Screenshot_20200302_223043.jpg
IMG_20200302_222959.jpg