Easy book on kanji / word etymology


I am searching for a book (preferably in Japanese, English also okay) on kanji
and / or word etymology. Basically I am looking for something that explains
the origin of words, for example: why is 馬鹿 written with horse and deer. Or
why does 虹 consists of the insect radical. I know "学研新漢和大字典 普及版", but it's
still too hard, so I am looking for something around the level JLPT-2.
Children's books are also welcome of course ;) Thanks a lot!

