I can suggest two book series that cover a range of science topics for 4 to 6 year-olds.
Both series offer titles on a wide range of topics, including the geology, weather, outer space, insects, etc.
If a child is naturally highly interested in such topics, the Let’s-Read-and-Find-Out Science series, which has a clean, straightforward approach in its writing and illustrations, may be sufficiently appealing to that child.
If on the other hand the child has not shown himself or herself to be keenly interested in such topics, then The Magic School Bus series might be a better choice because the books detail intriguing adventures of an eccentric teacher Ms. Frizzle and her students on their “magic school bus” that transforms itself into all types, shapes, and sizes of vehicles to explore any type of realm.
Of course, young children who are already very interested in the natural world will also enjoy The Magic School Bus as well.
Some of The Magic School Bus books have a lot of quote bubbles and other secondary text in addition to the main text, but parents can choose to ignore that content without losing much of the value of the books if they prefer just to read the main story line.