My friend Chloe loaned me her copy of Science is Simple: Over 250 Activities for Preschoolers; Katherine and I love it.
What I like best about Peggy Ashbrook's approach is her emphasis on helping kids learn to think like scientists rather than merely memorize scientific facts. Her activities are designed to develop inquisitive habits of mind where students observe, anticipate, and discover for themselves.
I am a strong proponent of classical education (as you can see in the sidebar links), but classical education theories and practitioners can tend to focus too exclusively on memorization in the grammar stage (elementary grades) to the neglect of creativity, imagination, and conceptual formation.
I think we often underestimate what children can grasp and do. As I've stated elsewhere, I'm pretty sure the stages of child development are permeable rather than rigid and static. While I do think the grammar stage should be heavy on fact absorption, I would hate to deprive my children of the joy discovery and imagination during those magical childhood years.