Written Japanese ordinarily doesn't use any spaces to separate words. But Japanese children's books do.
For example, the opening of Tomi Ungerer's The Three Robbers (すてきな 三にんぐみ)
くろマントに、 くろい ぼうしの さんにんぐみ。
それはそれは こわーい、 どろぼうさまの おでかけだ。
Are there general rules by which spaces would be inserted? (For example, always after particles, always at "word boundaries" (suitably defined).) Or do editors/authors just insert spaces at "natural" reading pauses? (Natural for small children at least.)
For example, in the same book きがついた is written without spaces (which would be fine if the rule were "no spaces in phrases which are a unit"), but then だれも かれも is written with space, but I think of the phrase as a unit.