'Why is the sky blue?!' 'Why birds can fly?' There are a number of questions that children may ask you but it is not always easy to answer appropriately.
Here is a great book that both children and parents enjoy reading together, called 'Naze? Doushite? Kagaku no Ohanashi' (Why? How? Stories for Science) It is written in Japanese and a series of books are designed for each school years.
There are about 40 short stories about body, living creatures, food and earth and it takes about 10 minutes for children to read each stories.
I like the stories of 'why is poo brown?' 'Why we shouldn't put tap water in golden fish bowl?' 'How milk turns to yogurt?' etc. etc.
It is highly recommended book for children!