These books are a great example of this:
The yellow one is from the "Erst ich ein Stück, dann du" ("It's my turn first, then yours" which is a terrible name in English but works nicely in German.) The one on the left is from the similar "wir lesen zusammen" ("Reading together") series. There are lots of books like this available here for early readers. They are meant to be read by parents and kids together, each reading their own passages aloud.
As soon as you open the book, you can figure out who should read which part. The adult segments are more difficult to read and in a smaller font, while the children sections are in a larger easier-to-read font and use vocabulary kids are familiar with, as you can see in this example from the "Geheimnisvoller Besuch in Klasse 1" book above.
Our family has truly enjoyed these books as Rebecca has been learning to read. Her passages are long enough that she is proud about contributing to the story, yet short enough that she doesn't get bored. Incorporating adult sections means that the stories can be more complex and flow better than elementary books alone can. The stories aren't as watered down for the early reader. There are even versions of classic books, such as Heidi and The Jungle Book
I have done a few Google searches and found some similar English books, but nothing seems to be from a major publisher or available in most bookstores. So to all of my writer friends, get on it! This is such a great idea, and I bet American kids would love it, too. (I'd do it myself, but this blog is already pushing the limits of my creative talent.)
If you are interested in the German versions, you can find them on Amazon:
"Erst ich ein Stück, dann du" on Amazon
"Wir lesen zusammen" books on Amazon