Fiction.

I got it at a church bazaar in 1968.

It had a dark brown hard cover.

Paper quality was smooth, semi- shiny.

In the story, children were complaining to parents that they didn’t want to sleep, and play longer. In the night a witch/sorcerer/elf kidnapped them and took them to his land, where children were not allowed to sleep. When they were sleepy, he would not allow it. They had to stay awake.

A child escaped/ rescued by angel-type, and went to angel type area, where they were allowed to sleep. They became soldiers against the witch. They were strengthened by drinking milk.