As a kid, my mom got me a flip book of body systems - nervous, circulatory, muscular, organs...i loved it. My son couldn't care less about a similar book :) so

As a kid, my mom got me a flip book of body systems - nervous, circulatory, muscular, organs...i loved it. My son couldn't care less about a similar book :) so in my experience its about offering things until you see they latch on and then you can explore the age appropriate depth they will enjoy rather than it being "school" time.