Every week, at the local grocery store, a new volume would be available for purchase, covering a new subject area (Anatomy, Animals, Aircraft, Watercraft, Electricity, Space, Weather, etc.). I was obsessed. I re-read all 15 of them countless times.
30+ years later, I bought a set off ebay in great shape to read with my kids. Seeing the diagrams and pictures I realized it was the source of many of the facts I know today.
You never know what's going to have an impact on your kids helping them realize what they are (going to be) interested in!