Hi, along with the bookshelf in your setting and the information you'll find on the back of each book cover,
amazon can also help with this!
Authors write books aimed at specific age group and this usually guides how much text is included in the book, what size and how many pictures appear in it, the complexity of the message the author wants to share with the reader, how detailed to story is and which words and language is used.
For example you would probably buy
board books, bath and cloth style books for very young children who enjoy the colours, texture, page turning and chewing them!
Toddler, preschool books can be paper or hardbacked, large informative pictures tend to be the main focus with simple words and sentences accompanying them.
In reception keystage 1 (if you work in england) books feature an increasing amount of text as children's reading skills develop. Gradually text takes over from pictures and stories become more intricate.
If you use the books in your placement you'll be able to see which books are age and stage appropriate for you children's needs.
Best wishes