The most common and most likely answer to this crossword clue is the 6 letter word POP-UP
I've seen this crossword clue in The Times
P
O
P
-
U
P
More clues leading to the result POP-UP
- Temporary pianos evenly sited round old university
- Work chewed by dog? Such may be children's book
- Stern-faced little pet in toddler's book?
- Appearing when option’s selected, champers at an end
- Flower mostly around middle of January opening quickly but temporarily
- Temporary work welcomed by young boxer?
- Father on horseback in 3-D picture book
- Publicity head's work on show – a kind of online ad
Buddy explains!

The straight part
We know that "Such may be children's book" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case such may be children's book = pop-up.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POP-UP mean?
POP-UP noun- Anything that pops up, particularly
- Coming into view suddenly from a concealed position.
- Opening out to form a three-dimensional structure when the page of a book is opened.
- Operating or existing for a brief period only; temporary.