This is the 10819th most frequent Polish word.
dziecięcych
The Polish word "dziecięcych" means "children's" or "childish" (genitive or locative plural form, or genitive singular feminine form).
In this sentence, "dziecięcych" is an adjective derived from "dziecko" (child), used in its genitive plural form to describe stories related to children.
Lubię czytać książki o historiach dziecięcych.
I like reading books about children's stories.
Here, "dziecięcych" is an adjective modifying the noun "zabawek" (toys), indicating the toys are associated with children.
W muzeum była wystawa zabawek dziecięcych sprzed lat.
There was an exhibition of children's toys from years ago at the museum.
In this context, "dziecięcych" describes "chorób" (diseases), signifying that these diseases are commonly associated with children or occurring in childhood.