I recently bought a copy of Bonjour Berthe by Gwen Brookes, which is a beginner French reader aimed at young children. I found the book charming, and I believe it would appeal to children in early primary school.
The book is a soft cover pamphlet with glossy pages. There are 13 pages of story, with each page having a large illustration and 1-2 sentences. The font is large and the quantity of text is minimal, at approximately 80 words in total. The sentences are in present tense with simple structures. The vocabulary density is around 50%, which indicates enough repetition to allow some learning of vocabulary. However, the text is so short that the only words to get at least 5 appearances are “est” and “elle”, so many books would need to be read to provide learning purely from reading. Instead, the book includes activities (a wordsearch and a game) to improve vocabulary retention. All words are translated in a glossary at the end of the story.
If you are looking for books for early primary school aged children learning French, this series is a good choice.