These use six- and eight-fold symmetry across three rings, which gives roughly twenty large shapes per page. A shape has to be big enough to fill without going outside the line, and that is the whole design constraint at this age.
Lines are thick, so the boundary stays visible under a crayon rather than disappearing beneath it.
The centre is a small rosette rather than a point where every petal converges. Petals that all meet in the middle print as a solid blot of ink, which is unusable.