Whilst out and about last week we needed to find a toilet and stumbled upon the library at the Wasserturm in Prenzlauer Berg. As you can see from the pictures below the children's section is great! They have a minute section of English books but for many of us once children start at Kita or school they will be needing German books anyway.
It galvanized me into joining the library system here. It costs 10€ a year for adults to join (and is free for children) and your library card gives you borrowing rights in any library in Berlin. I was asked for my passport and a proof of address here in Berlin to join.
For more information about libraries in Berlin visit the Stadt Bibliothek website to find your local libraries.
Once you are a member you can search for, renew and reserve books at www.voebb.de which has information in English.