This particular series pictured is actually 6 stories per volume, about 14 pages per story, but you are correct that each page only has between 1 and 3 sentences at Level 0. There are fewer stories/books per volume with more pages per book and many more sentences per page as the Level increases. They do also come with a CD, so I use them initially for listening practice before doing any reading.
They are not actually kids’ books, they are written specifically for foreign learners of Japanese - while the graphics in the lower levels make them look like children’s picture books, the intention is that the visual cues will mean you will not need a dictionary even if you encounter new vocab - you will be able to guess the meaning from the visual context.
@ericky14 There is a club for people working their way through graded readers and parallel texts here if you’d like to join us (I’m working on the Level 0 readers at the moment).