I'm reading the book which was written for young child  a children's book *OR* a book written for children. The book name book is called Magic tree house. 

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Although this story is so very childish, I will read it to the end for improving to improve my English.

Chapter 1.
Jack is Annie's older brother. He is eight and a half years old, Annie is just seven years old. 
Annie loves pretend stuff but Jack likes real things.
One day, they went into the woods and discovered a tree house that is was ('went' was used, which is past tense, so this should also be past tense) filled with books.
Actually, Jack didn't want to go up into the tree house but he has had (past tense) no choice because he loves books.

**"I'm reading a children's book called Magic tree house" would sound more natural

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Good job! :) Keep reading, it helps a lot, and children's books are a great place to start :)

Magic treehouse

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Hi! Good effort here! Reading books is a great way to improve your English :) just be careful with comma placement and verb forms.

Hope this helps!