This is the 890th most frequent Russian word.
детских
"Children's" or "of children."
The word 'детских' is used as an adjective in the genitive plural case, agreeing with the plural noun 'садах' (kindergartens), to specify the type of kindergartens.
Я работаю в детских садах.
I work in kindergartens.
Here, 'детских' describes the noun 'книг' (books), indicating that the books are intended for children.
Моя сестра занимается продажей детских книг.
My sister sells children's books.
In this sentence, 'детских' modifies 'комнат' (rooms), signifying that the rooms are designed for children.