Scholastic Science Readers by Lily Wood

These books have simple language and short sentences for beginning readers. These three books were published under the pen name, Lily Wood.
Bats is for Level 1, ages 5 and 6. 0-439-29585-8
Volcanoes is for Level 2, ages 7 and 8. ISBN 0-439-29582-3
Skeletons is for Level 2, ages 7 and 8. ISBN 0-439-29586-6
These are also available in a sturdier edition with different ISBN.