While choosing books for your 6- to 7-year-old, it’s helpful to consider how your child will experience the titles — namely, whether you will read to him (read-alouds), whether you will read books together (read-withs), or whether he will read them on his own (read-alones).
A read-aloud book is one that you read to your child at special times — like bedtime or in a comfy chair on a rainy afternoon. These books should always be well above your child's independent reading level because you are the one in control of the reading.
A read-with book is one that you and your child read together. Now, however, the primary control of the book is in your child's hands, as for the most part your child will be the one reading aloud. These books should be generally at or slightly above your child's independent reading level. As your child reads aloud to you, you can offer help as needed with difficult words or phrases.
A read-alone book is just that — a book that your child selects and then reads on her own, perhaps at night after spending earlier time with a read-aloud. The key to book selection here depends upon the broad foundation you set in the above experiences. You can take your child to the library and point out books by the authors you both have already read together or explore topics of interest you have discovered together.
As your kids get older, they will naturally want to assume greater control over the selection of reading materials they encounter. Encourage this — it's a good indicator of your child's desire and motivation to read proficiently. Proficient readers are most able to read for enjoyment and learning.