Screen Time won’t turn off for my child

I had Screen Time enabled for both my kids. Today I wanted to turn it off. For one child this worked just fine: I went to the child’s Screen Time settings on my iPhone and click the “Turn off Screen Time” button and done. Most of the Screen Time settings UI disappears and there’s only a button to enable it again.

However, for my other child this doesn’t work. When I click “Turn off Screen Time” nothing happens. I also tried on his phone, but there is no Turn off Screen Time button in his settings. Maybe because it is managed from my phone/account.

Does anybody know what’s going on?